Week 9 Flashcards
Acid, Base, pKa, buffer
Acid = proton doner
Base = proton acceptor
pKa = the pH at which 50% of molecules are ionised (= -log Ka)
Strong acid: Ka>1 ,pKa<0
Weak acid: Ka<1, pKa>0
Buffer solution = a solution that resists change in pH when small amounts of acids or alkalis are added
Weak acids or bases that exist at equilibrium with the conjugate
If pH of blood flucturates by 0.5 = fatal
Henderson-Hasselbach equation and clinical implications
= an equation relating the pH, pKa and ratio of the concs of acid and base in a solution
Many drugs are weak acids or bases
Un-ionised drugs cross membranes and enter the blood stream more easily
The environment (acidic/basic) will impact the ratio of ionised and unionised drugs
Major buffer systems in the blood
Protein buffers:
Increase in pH – carboxyl group can act as weak acid and dissocate, become a carboxylate ion
Decrease in pH – Carboxylate group and amino group can act as weak bases and accept a proton forming a carboxyl group and an amino ion
e.g. histamine and cysteine are important in ISF and ECF
Hb buffer system:
Protons produced in the conversion of CO2 to HCO3- ions are buffered by haemoglobin
Phosphate buffer system:
Important in urine, skeletal muscle cells and ICF
Closed system
Phosphates act as buffer
Bicarbonate buffer system:
Most important ECF buffer system
Open – can excrete waste via lungs and kidneys
alkalosis and acidosis
Respiratory acidosis = increased CO2 -> carbonic acid -> decreased pH
Respiratory alkalosis = excessive elimination of CO2 -> decreased carbonic acid -> increased pH
Metabolic acidosis= loss of bicarbonate ions -> increased H+ -> decreased pH
Metabolic alkalosis = increased bicarbonate ions -> decreased H+ -> increased pH
Methods of evaluation cardiac function and ventilation
Arterial blood pressure -
Invasive measurement:
Insert cannula into peripheral artery
Reported as systolic/diastolic (mean)
Non-invasive measurement:
Sphygmomanometry – pressure cuff
Oscillometric
Doppler
Central venous pressure -
Measures blood returning to right side of heart
ECG-
Heart rate and rhythm
Blood oxygen content -
Mucous membrane colour
Blue/cyanosis = bad
Pulse oximetry -
Measures oxygenated haemoglobin
Blood gas analysis
Capnography
CO2 measurements for info on lung and heart metabolism
Advantages and disadvantages of pulse oximetry
Disadvantages:
Doesn’t measure oxygen carrying capacity
Not effective on anaesthetised animals as they receive 100% oxygen
Cannot identify smoke inhalation e.g. CO poisoning
Advantages:
Cheap
Fast
accurate
Effect of exercise on cardio and respiratory function
Breathing rate is dictated by piston pendulum mechanism
Lungs are compressed and decompressed forcibly by the diaphragm during movement
At a gallop horses cannot increase breathing rate as their stride rate is at its peak, they can only increase their depth of breathing
Blood gas barrier gets thinner with exercise and training to improve efficiency of gas exchange
Cardio system:
Increased CO
Increased O2 carried in blood (more RBCs from spleen -> increased PCV)
Redistribute blood flow
disorders of the equine respiratory system
Resistance to air flow:
Horses can only breathe through their nostrils
Reduced diameter of airways e.g. asthma
Laryngeal hemiplegia:
Partial paralysis of larynx
Inadequate gas exchange
Decreases airflow to lungs + causes exercise intolerance
Dorsal displacement soft palate:
Loud expiratory gurgling noise
Reduces VO2 max
Hypoxia and Hypercapnia Definition and causes
Hypoxia = inadequate oxygen supply to tissues and organs
Causes:
Low levels of O2 in arterial blood
Reduced oxygen carrying capacity due to anaemia or decreased Hb levels
Inadequate blood flow
Tissues unable to utilise available oxygen
Hypercapnia = build up of CO2 in the blood
Causes:
Impaired ability to remove CO2 from lungs
Increased CO2 production due to excess or impaured metabolism
