Respiratory Physiology Flashcards
What is a right to left shunt in terms of pulmonary circulation?
A right to left shunt occurs when venous blood bypasses the pulmonary capillary circulation, mixing with blood from exchanging alveolar units. A small degree of shunt can occur from venous drainage from the larger airways (entering the pulmonary veins) and from the coronary circulation (entering the LV via the Thebesian veins).
A large shunt can occur in congenital heart disease eg ASD, VSD, pulmonary AV fistula. This can lead to significant arterial hypoxaemia. In this case the response to administration of 100% O2 will be much less than expected.
Define TLC and name conditions in which it is increased/decreased
TLC is Total Lung Capacity, the volume of gas contained in the lungs after maximal inhalation.
TLC = IRV + Vt + ERV + RV
TLC = IC + FRC
TLC increases in swimmers (increased insp muscle strength), and in emphysema (decreased elastic recoil)
TLC decreases in conditions with increased elastic recoil (IPF, cardiac failure), chest wall stiffness (neuromuscular disease, obesity, pregnancy), or thoracic space reduction (pleural effusion)
Define RV and the impact of restrictive and obstructive conditions on RV
RV is Residual Volume, the volume of gas that remains in the lungs after maximal expiration.
In restrictive conditions RV reduces due to increased lung elastic and chest wall recoil, and loss of parenchyma
In obstructive conditions RV increases due to premature airway closure, decreased lung elastic recoil, and dynamic increase in expiratory flow limitation.
Which lung volumes can be measured directly, and which require special techniques/calculations?
Directly:
* VC (vital capacity)
* Vt (tidal volume)
* IC (inspiratory capacity)
* EILV (end inspiratory lung volume)
* EELV (end expiratory lung volume)
Special techniques/calculations:
* TLC (total lung capacity)
* RV (residual volume)
* FRC (functional residual capacity)
Define TLCO (DLCO) and name conditions in which is is increased and decreased
TLCO is the transfer factor of the lung for carbon monoxide. It measures the surface area available for gas exchange.
TLCO is the amount of CO absorbed per unit time and per unit CO partial pressure.
CO uptake is independent of blood flow but is dependant on Hb binding sites.
TLCO is measured during a 10s breath hold at maximal inspiration.
TLCO is dependant on both Va (alveolar volume) and KCO (rate of alveolar uptake of CO).
Increase TLCO:
* increased cardiac output
* pulmonary haemorrhage
Decrease TLCO:
* Anaemia
* loss of Va due to emphysema or ILD (TLCO and KCO reduced)
* extrathoracic restriction eg resp muscle weakness (TLCO reduced, KCO increased)
* loss of Va due to pneumonectomy or consolidation (TLCO reduced, KCO increased)
* airflow obstruction
Name causes of normochloraemic and hyperchloraemic metabolic acidosis
Normochloraemic metabolic acidosis (high anion gap):
Ketoacidosis
Lactic acidosis
Renal failure
Toxins
Hyperchloraemic metabolic acidosis (normal anion gap):
Extra-renal sodium loss
Renal tubular acidosis
List causes of metabolic alkalosis
Gastric fluid loss
Volume contraction
Mineralocorticoid disorders
Milk-alkali and Bartter syndromes
Hypoalbuminaemia
List causes of Respiratory Acidosis
CNS depression eg head injury, opiate overdose
Neuromuscular disorders
Chest wall abnormalities
Lung diseases
List causes of Respiratory Alkalosis
Anxiety
CNS disorders
Hormones/drugs (catecholamine, progesterone, hyperthyroidism, salicylate)
In the context of CPET what is VO2max?
VO2max is the maximal oxygen uptake of skeletal muscle during exercise. If the subject puts in sufficient effort it is a good test of maximal aerobic capacity. It reflects a limitation in oxygen conductance from lungs to mitochondria. Limitation may be related to stroke volume, heart rate or tissue extraction. <80% is abnormal, and <40% is severe impairment.
In the context of CPET, what is the ventilatory anaerobic threshold?
Anaerobic threshold is the highest VO2 at which the arterial lactate does not systematically increase. It is as estimate of exercise capacity. In the initial, aerobic phase of the CPET protocol (up to 50-60% VO2max) expired ventilation (VE) increases linearly with VO2 and reflects aerobically produced CO2 in the muscles. Blood lactate does not change much in this phase. In the latter phase of the CPET protocol anaerobic metabolism occurs as oxygen supply cannot keep up with the demands of exercising muscles. There is a significant increase in muscle lactic acid production and a rise in blood lactate. The VO2 at the onset of blood lactate rise is called the Ventilator Anaerobic Threshold.
In the context of CPET, what is RER?
RER is Respiratory Exchange Ratio. It is the ratio of carbon dioxide output to oxygen uptake (VCO2/VO2). Under steady state conditions the RER equals the RQ (Respiratory Quotient). RQ is determined by fuels used for metabolic processes - RQ of 1 indicates carbohydrate metabolism. RQ <1 indicates a mixture of carbohydrates and fat and/or protein. In steady state the blood and gas transport systems keep pace with tissue metabolism so RER measured a the mouth can be used as a rough index of RQ. RER increases during exercise due to buffered lactic acid and/or hyperventilation.
In the context of CPET what is the oxygen pulse?
Oxygen pulse is the product of the stroke volume and the difference between arterial oxygen content and mixed venous oxygen content. It can be calculated as: Oxygen pulse = VO2 / Heart rate
Oxygen pulse may be low at peak exercise in ILD due to reduction in stroke volume and arterial oxygen content.
In the context of CPET what is heart rate reserve?
HRR (heart rate reserve) is the difference between the predicted peak heart rate (for age) and peak heart rate achieved in the CPET. In healthy people HRR is close to zero. A high HRR may be seen in COPD, ILD, and CF.
Name direct and indirect methods of bronchial hyper responsiveness testing.
Direct:
Methacholine
Histamine
Indirect:
Exercise testing (+/- dry or cold air)
Inhaled AMP
Inhaled mannitol
Eucapnic Voluntary Ventilation (EVV)
