Physiology Flashcards

1
Q

Which of the following would MOST likely be found in a patient with cyanide toxicity?

A

The most common and reliable sign of cyanide toxicity is an anion gap metabolic acidosis.

TrueLearn Insight : Anion gap is calculated by subtracting serum chloride and bicarbonate (anions) from serum sodium and potassium (cations). Anion gap = ([Na+] +[K+]) – ([Cl−] + [HCO3−]). In clinical practice, potassium is usually excluded.

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2
Q

Which of the following may be associated with INCREASED mixed venous oxygen saturation?

A

Mixed venous oxygen saturation (SvO2) is an indicator of global oxygen supply and demand balance. A low SvO2 indicates increased tissue oxygen extraction due to decreased oxygen supply relative to the demand. Septic shock and cyanide toxicity are conditions associated with normal or increased mixed venous oxygen saturation secondary to impaired tissue oxygen utilization.

TrueLearn Insight : Central venous oxygen saturation (ScvO2) measured by sampling blood through a central venous catheter located in the superior or inferior vena cava is often higher than SvO2. This is because of the venous blood with significantly low oxygen saturation entering from the coronary sinus and mixing in the right atrium.

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3
Q

Which of the following patients would be LEAST likely to have pronounced upregulation of nicotinic acetylcholine receptors?

A

Upregulation of NAChR’s is seen in spinal cord injuries, burn patients, prolonged immobilization, stroke patients, patients with neuromuscular disorders, and after prolonged exposure to certain pharmacologic agents.

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4
Q
A 50-year-old man weighing 70 kg is in the critical care unit after a motor vehicle accident in which he experienced multiple rib fractures, thoracic spine fractures, and pulmonary contusion bilaterally. He is currently intubated with the following ventilator settings:
Mode:  Volume control
Tidal volume:  700 mL
Rate:  10 breaths per minute
PEEP: 8 cm H2O
FiO2: 70%
Peak inspiratory pressure: 30 cm H2O
Plateau pressure: 30 cm H2O
The patient has no intra-abdominal injuries, MAP is >70 mm Hg on no vasopressor or inotropic support, and he has no past medical history. Hemoglobin is 12 g/dL, creatinine is 1.6 mg/dL, and urine output is declining.  Which of the following is MOST likely true?
A

Positive pressure ventilation exerts deleterious effects on renal function via alterations in hemodynamics, neurohormonal secretion, and biochemical mediator release.
Decreasing the tidal volume to 6 mL/kg (lung-protective strategy) could decrease the risk of renal injury related to positive pressure in the patient in this question by decreasing cytokine release.

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5
Q

Which of the following hormones is LEAST likely to be metabolized by the lungs or within the pulmonary circulation?

A

Dopamine, epinephrine (B), and histamine are not metabolized or removed from the pulmonary circulation since the pulmonary endothelium lacks an active transport mechanism for these hormones.

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6
Q

Sympathetic cardiac innervation includes which of the following adrenergic receptors?

A

The sympathetic cardiac innervation originates from T1-T4 and is associated with α1, β1, and β2 adrenergic receptors.

TrueLearn Insight : A left stellate ganglion block can be performed to reduce the risk of arrhythmias associated with long QT syndrome.

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7
Q

A 22-year-old man eats sausage from an expired and bloated can. A day later he develops trouble swallowing, muscle weakness, blurred vision, constipation, and dry mouth. On examination he is found to have decreased deep tendon reflexes. Which of the following is the toxin’s correct mechanism of action?

A

Botulinum toxin can cause symptoms of muscle paralysis by preventing the release of acetylcholine-containing vesicles from the axon terminal into the synaptic cleft.

TrueLearn Insight : Botulinum toxin acts inside the axon terminal at the neuromuscular junction. Tetanus toxin travels via retrograde axonal transport to the CNS where it acts.

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8
Q

Which of the following will cause a decrease in the P50 of oxygen?

A

A leftward shift, moving the curve to the left, results in a decrease in P50; oxygen affinity increases leading to less offloading of oxygen in the tissues at all PO2 values. This will occur under several circumstances - alkalosis, decreased temperature, decreased intracellular concentration of organic phosphates (the most important is 2,3-diphosphoglycerate in the red blood cells), carbon monoxide binding, and the presence of methemoglobin. A rightward shift is the exact opposite and will result in more oxygen offloading in the tissues at all arterial oxygen tensions (PO2). Rightward shift is seen with acidosis, increased temperature, and increased organic phosphate concentrations. The Bohr effect states that oxygen is more readily released from hemoglobin in the face of acidosis or hypercarbia.

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9
Q

During a mitral valve repair and separation from cardiopulmonary bypass, the cardiac anesthesiologist determines the systemic vascular resistance to be 600 dynes per sec/cm5 with a central venous pressure of 22.5 mm Hg. As a result, norepinephrine is started.

Consequently, starting the norepinephrine infusion resulted in the following changes: the mean arterial pressure by arterial line increases from 45 mm Hg to 75 mm Hg, and cardiac output via thermodilution increases from 3 L/min to 3.5 L/min. Assuming the central venous pressure stays the same, how does the systemic vascular resistance change?

A

Systemic vascular resistance (SVR) is calculated as SVR = 80 × (MAP – CVP) / CO (CO, cardiac output; CVP, central venous pressure; MAP, mean arterial pressure).

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10
Q

Which of the following numbers corresponds to the most significant efflux of potassium from the myocyte during an action potential?

A

The influx of sodium in phase 0 causes membrane depolarization.
The net influx of calcium in phase 2 causes a plateau.
The efflux of potassium in phase 3 causes membrane repolarization.

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11
Q

Which of the following best describes the Haldane effect?

A

The Haldane effect explains the increased ability for hemoglobin to carry carbon dioxide (CO2) from the tissues to the lungs for exhalation

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12
Q

Which of the following is NOT true regarding the stress response and lipolysis?

A

Lipolysis is the hydrolysis of triglycerides into glyceride and free fatty acids which are then used as an energy source. In general, lipolysis is increased by beta-2 and beta-3 adrenergic stimulation but is inhibited by alpha-2 stimulation. Women are more sensitive to the lipolytic actions of catecholamines when compared to men. Increased catecholamines, cortisol, and glucagon secretion all promote lipolysis. Alpha-2 stimulation will inhibit lipolysis.

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13
Q

Which of the following is the MOST likely cause for the rapid reduction in core temperature during the first hour of general anesthesia?

A

Redistribution of heat from the core to the periphery is the largest contributor to the initial reduction in core temperature during general anesthesia. Prevention or reduction of this can be accomplished by pre-warming the patient’s extremities prior to the induction of general anesthesia. Radiation is the main mechanism for patient heat loss in the operating room following this initial redistribution of heat.

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14
Q

Which of the following will result in a leftward shift and increased slope of the carbon dioxide ventilatory response curve (i.e. a change from the black to the red curve)?

A

Surgical stimulus and heightened states of arousal (e.g. fear or anxiety) cause hyperventilation. This typically causes a leftward shift and increased slope of the carbon dioxide ventilatory response curve (VRC).
Factors that cause a leftward shift and an increased slope of a carbon dioxide ventilatory response curve include arterial hypoxemia, metabolic acidemia, surgical stimuli, and certain CNS pathologies. Factors that cause a rightward shift and a reduced slope of the curve include opioids, barbiturates, and sedative-hypnotic drugs. Volatile anesthetics ≤1 MAC cause a rightward, parallel shift of the VRC.

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15
Q

Which of the following is the dominant factor in causing bronchoconstriction?

A

The parasympathetic nervous system contributes a great deal to bronchoconstriction. The etiology behind bronchoconstriction is only partially known and research is ongoing.

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16
Q

Which of the following is TRUE regarding type 2 diabetes mellitus?

A

Insulin deficiency occurs secondary to a loss of beta-cell mass in the pancreas. A lack of insulin results in hyperglycemia and the symptoms associated with diabetes mellitus. Insulin deficiency can recover, at least partially, in patients with improved glycemic control.

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17
Q

Which of the following will MOST likely enhance hypoxic pulmonary vasoconstriction?

A

Since hypercarbia itself causes pulmonary vasoconstriction, the presence of hypercarbia in the setting of hypoxia enhances the effects of hypoxia pulmonary vasoconstriction (HPV).
Hypoxic pulmonary vasoconstriction occurs as a result of exposure of the pulmonary arteries to hypoxic lung segments and low alveolar oxygen tension. Direct inhibitors of the HPV mechanism include: hypocarbia, vasodilating drugs, infection, metabolic alkalemia, and volatile anesthetics >1 MAC. Indirect inhibitors of HPV include: hypervolemia, vasoconstricting drugs, hypothermia, thromboembolism, and a large hypoxic lung segment.

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18
Q

Which of the following is TRUE about the accumulation of hydromorphone metabolites in patients with end stage renal disease?

A

Many opioids have metabolites that accumulate in patients with renal insufficiency/failure and caution must be taken. Morphine has two major metabolites that accumulate, morphine-3-glucuronide (neuroexcitatory) and morphine-6-glucuronide (potent analgesic and respiratory depressant), hydromorphone’s metabolite is hydromorphone-3-glucuronide (neuroexcitatory), and meperidine’s is normeperidine (neuroexcitatory). Fentanyl is generally considered the safest opioid for use in renal failure patients due to a lack of active or toxic metabolites.

19
Q

A 45-year-old man in the intensive care unit is brought to the operating room for a tracheostomy. A modern anesthesia machine is being used with a circle system. Which of the following is MOST LIKELY to cause an INCREASE in dead space ventilation or dead space fraction?

A

Dead space is the volume of inspired air that does not participate in gas exchange. During anesthesia and mechanical ventilation, dead space ventilation or dead space fraction is increased with additions to the circuit on the patient side of the Y-piece connector (in other words, proximal, not distal, to the patient, between the Y-piece and unidirectional valves), when alveoli are hyperinflated, or when pulmonary perfusion decreases.
When tidal volume decreases, anatomic dead space remains the same; thus, the fraction of gas participating in gas exchange decreases and the fraction of dead space ventilation increases. When tidal volume equals the alveolar dead space, effective alveolar ventilation ceases.

20
Q

A patient has a respiratory system compliance of 100 mL/cm H2O and a lung compliance of 200 mL/cm H2O. What is the patient’s chest wall compliance?

A

The following formula summarizes the relationship of respiratory system compliance and its two components: 1/CRS = 1/CL + 1/CCW.

TrueLearn Insight : Chest wall compliance is relatively high in neonates due to a pliable rib cage. However, this increases work of breathing since the rib cage provides less mechanical support, which in turn leads to significant retractions and earlier functional airway closure.

21
Q

Rapid and excessive normal saline administration would MOST likely result in which of the following sets of lab values?

A

Excessive and rapid administration of normal saline can lead to a non-anion gap hyperchloremic metabolic acidosis with decreased plasma bicarbonate (HCO3-), increased plasma chloride (Cl-), and a decreased plasma strong ion difference (SID).
Therapy for saline-induced hyperchloremic acidosis consists of intravenous administration of a crystalloid solution with a high SID, such as sodium bicarbonate or tromethamine (“Tham” solution).

22
Q

Which of the following statements about aerobic and anaerobic glycolysis is TRUE?

A

Aerobic metabolism produces approximately 16 times the ATP of anaerobic metabolism. The additional ATP is produced within the mitochondrion via the citric acid cycle and oxidative phosphorylation. Both anaerobic and aerobic metabolism start with glucose, but anaerobic metabolism generates lactate while aerobic metabolism produces carbon dioxide and water.

TrueLearn Insight : In anaerobic glycolysis, the free energy of oxidation (NADH to NAD+) is wasted as heat, whereas in aerobic glycolysis 2.5-3 ATP are produced per NADH.

23
Q

A 67-year-old male with history of COPD is admitted to the pre-op area for an elective herniorrhaphy. The nurse notices his pulse oximeter to be 90% and places a nasal cannula at 4 L/min oxygen. You find that last week his blood gas pCO2 was 45 mmHg and you decide to confirm the number by drawing another sample. The resultant pCO2 comes back as 56 mmHg. Which of the following alterations is the cause for the observed hypercapnea in the setting of oxygen administration?

A

Hypercapnia following administration of oxygen to a patient with chronic obstructive pulmonary disease is primarily due to ventilation-perfusion mismatching, driven by inhibition of hypoxic pulmonary vasoconstriction.
In patients with COPD, hypoxic pulmonary vasoconstriction is the most efficient way to alter the V/Q ratios to improve gas exchange. This physiological mechanism is counteracted by oxygen therapy and accounts for the largest increase of oxygen-induced hypercapnia. A titrated oxygen therapy to achieve saturations of 88% to 92% is recommended in patients with an acute exacerbation of COPD to avoid hypoxemia and reduce the risk of oxygen-induced hypercapnia.

24
Q

An action potential at the muscle postsynaptic membrane is triggered through a sequence of events. Which of the following molecules is most involved in the first step of generating an action potential in a postsynaptic neuromuscular junction?

A

The opening of sodium channels on the postsynaptic terminal triggers an action potential.

25
Q

Assuming normal cardiopulmonary function, which of the following statements regarding the relationship of partial pressures (P) of inhaled anesthetics at equilibrium is CORRECT?

A

As long as normal cardiopulmonary function exists (i.e. no intrapulmonary, intracardiac, or cardiopulmonary shunting), PCNS = Pblood = Palveoli of inhaled anesthetics at equilibrium.

26
Q

During exercise, oxygen diffusion in the lung is increased by which of the following mechanisms?

A

Exercise increases oxygen diffusion by increasing lung surface area (thinner, more distended alveoli) and by increasing blood flow (capillary recruitment).

27
Q

A 72-year-old female with postoperative oliguria has a plasma osmolality of 294 mOsm/kg. Which of the following urine osmolality values suggests a prerenal cause to this patient’s oliguria?

A

A urine-to-plasma osmolar ratio (UOSM : POSM) >1.5 indicates prerenal oliguria (generally secondary to hypovolemia). In this patient, the urine osmolality would need to be >441 mOsm/kg (294 mOsm/kg x 1.5).

28
Q

Which of the following statements about bronchial smooth muscle tone is TRUE?

A

Stimulation of β2 adrenergic receptors causes bronchodilation while M3 receptor stimulation causes bronchoconstriction. Epinephrine causes significant bronchodilation. Norepinephrine does not cause significant bronchial smooth muscle relaxation as it is more β1-selective.

29
Q

Which of the following will MOST likely facilitate the release of oxygen from hemoglobin?

A

Bottom Line: A leftward shift of oxygen-hemoglobin dissociation curve is caused by a decrease in temperature, PaCO2, hydrogen ion concentration, and 2,3-DPG. A rightward shift is caused by an increase in temperature, PaCO2, hydrogen ion concentration, and 2,3-DPG.

TrueLearn Insight : Remember the mnemonic “CADET Face Right”. Increase in CO2, Acid, 2,3-DPG, Exercise, and Temperature result in Right shift. Cadets prefer to unload their guns (oxygen).

30
Q

Which of the following compounds is synthesized by the liver?

A

Angiotensinogen is synthesized in the liver. The majority of clotting factors are synthesized and released from the liver with notable exceptions of factors 3, 4, and von Willebrand factor. Platelets are synthesized by megakaryocytes in the plasma.

TrueLearn Insight : Factor VIII is synthesized in the liver as well as endothelial cells. Thus, it remains at normal (or high) levels when other factors are deficient in liver disease.

31
Q

A patient is undergoing coronary artery bypass surgery. Intraoperatively, the surgeon has placed a catheter in the aorta to transduce the arterial pressure. Which of the following is most likely TRUE regarding the arterial pressure waveforms recorded at the proximal aorta compared to the radial artery?

A

Compared to the proximal aorta, arterial waveforms measured at more distal sites have the following characteristics: higher systolic peak, steeper systolic upstroke, lower diastolic peak, blunted dicrotic notch, delayed dicrotic notch, slightly lower MAP.

32
Q

Which of the following statements regarding carbon monoxide is CORRECT?

A

Carbon monoxide reversibly binds to hemoglobin with 200-300 times greater affinity than oxygen. Carbon monoxide reduces oxyhemoglobin concentration by displacing oxygen from the hemoglobin molecule and creating carboxyhemoglobin. Carbon monoxide does not affect the PaO2, the major substrate for carotid body receptors. Increasing PaO2 will increase total arterial blood oxygen content.

33
Q

An otherwise healthy 27-year-old man presents for video-assisted thoracoscopic surgery (VATS) with chemical and mechanical pleurodesis for the treatment of multiple spontaneous right-sided pneumothoraces. One lung ventilation is planned for this case. Which of the following is MOST TRUE regarding the distribution and regulation of pulmonary blood flow?

A

Pulmonary blood flow is characterized by a ten to fivefold lower blood pressure than the systemic circulation due to a multitude of factors including shorter and wider blood vessels, less vascular smooth muscle making the vessels more distensible, and extremely thin capillary cell membranes which allow the capillaries to participate in gas exchange. Gravity has a significant effect on both the quantity and quality of blood flow through the lungs as described in the so-called ‘West Zones’. Hypoxic pulmonary vasoconstriction acts to decrease shunt fraction by diverting blood away from hypoxic lung regions to more well-ventilated portions of the lung.

34
Q

Which of the following would decrease left ventricle coronary perfusion pressure?

A

CPPLV = AoDP - LVEDP. Hemodynamic variables that increase LVEDP will decrease CPP.

Autoregulation of CBF is compromised with coronary stenosis. Autoregulation fails first in the subendocardium, resulting in subendocardial ischemia and ST segment depression.

35
Q

Which of the following statements regarding the renin-angiotensin-aldosterone system is CORRECT?

A

Renin is produced in the kidneys in response to decreased renal perfusion and cleaves angiotensinogen into angiotensin I. Angiotensin I is converted to angiotensin II by ACE in the lungs and kidneys. Angiotensin II then promotes aldosterone production. Angiotensin II and aldosterone both act to increase intravascular volume, raise systemic blood pressure, and maintain adequate GFR.

36
Q

A 52-year-old male presents for an open inguinal hernia repair under general anesthesia. Which of the following is MOST likely to reduce renal blood flow?

A

he sympathetic nervous system provides baseline vascular tone in the kidney and when activated causes vasoconstriction that can decrease renal blood flow.

TrueLearn Insight : Inhaled anesthetics cause a transient reversible depression in renal function. GFR, renal blood flow, urine output, and urinary excretion of sodium are decreased

37
Q

After breathing 100% oxygen for ten minutes, which of the following approximates how long an upright healthy 70 kg adult patient can remain apneic before becoming hypoxemic?

A

Adult oxygen consumption = 3-4 mL/kg/min, FRC of any healthy patient = 30 mL/kg. Functional residual capacity becomes the sole source of oxygenation during apnea.
[FRC (mL) ÷ O2 consumption (ml/min)] * %O2 in FRC = minutes until hypoxemia

38
Q

Which of the following values is NOT required to calculate static respiratory system compliance?

A

Static respiratory system compliance is calculated using the following formula: CS = VT ÷ (PPL – PEEP).

TrueLearn Insight : Elastance is the inverse of compliance: E = ΔP/ΔV.

39
Q

A 60-year-old male is scheduled for laparoscopic cholecystectomy. He has a 3-year history of diabetes mellitus as well as hypertension, treated with regular insulin and propranolol. The patient reports taking his medications prior to coming to the hospital. You receive a call from the nurse in the preoperative area that the patient has a glucose of 40 mg/dL. Regarding this hypoglycemic episode, which of the following is MOST likely to be seen in this patient?

A

Sweat glands are innervated by the sympathetic nervous system and utilize acetylcholine with muscarinic receptors, therefore beta blockade will not prevent sweating with hypoglycemia which may be the only symptom seen in this setting.

40
Q

A 75-year-old patient with chronic obstructive pulmonary disease presents for liver biopsy. Which of the following is more useful in determining the synthetic function of the liver in this patient?

A

The liver is extremely important in synthesizing several important proteins. Biochemical testing to determine the liver’s synthetic capability is important for evaluation of patients however, no perfect test has been found. Albumin and prothrombin time are used currently.

TrueLearn Insight : There have been many studies attempting to classify cirrhosis and predict outcome; Child-Pugh-Turcotte classification and the Model for End stage Liver Disease (MELD) are the two most common used. Child-Pugh-Turcotte uses total bilirubin, albumin, prothrombin time (PT)/international normalized ratio (INR) and the presence of ascites or hepatic encephalopathy. MELD uses serum bilirubin, creatinine, international normalized ratio (INR) for prothrombin time. MELD is more accurate predictor of short-term mortality. Both of these are used to help determine transplantation priority. The Child-Pugh scoring system has variables that are considered reflective of the synthetic function of the liver – albumin and prothrombin time.

41
Q

Which of the following will lead to increased oxygen delivery?

A

Oxygen delivery is determined by CO and CaO2. Increases in HR, SV, and BP increase cardiac output and therefore DO2. Cardiac output and DO2 are inversely proportional to SVR. Increases in SaO2, Hb, and PaO2 increase CaO2 and therefore DO2.

42
Q

Which of the following is a source of tissue hypoxia from carbon monoxide poisoning?

A

Carbon monoxide poisoning causes tissue hypoxia and acidosis by decreased coupling of oxidative phosphorylation, a leftward shift of the oxygen-hemoglobin dissociation curve, decreased ATP production, and increased lactate production

43
Q

Systemic vascular resistance in dynes * sec/cm^5 = [80 * (MAP – RAP)] ÷ CO. Central venous pressure is commonly substituted for RAP. Conversion of dynes * sec/cm^5 to Woods units may be achieved by dividing SVR by 80. For example, 1520 / 80 = 19 Woods units.

A

Pulmonary vascular resistance in dynes * sec/cm^5 = [80 * (MPAP – PAOP)] ÷ CO. Conversion to Woods units may be achieved by dividing by the conversion factor of 80. For example, 128 / 80 = 1.6 Woods units (mm Hg/L/min)