Animal Physiology

1. A carbohydrate overload model was used in 8 horses to evaluate Starling forces and hemodynamics of the digit during the prodromal stage of acute laminitis.A pump-perfused extracorporeal digital preparation was used to evaluate blood flow, arterial pressure, venous pressure, capillary pressure, isogravimetric capillary filtration coefficient, osmotic reflection coefficient, and vascular compliance. From these data, pre- and postcapillary resistances and pre- to postcapillary resistance ratios were determined. Vascular and tissue oncotic pressures were estimated from plasma and lymph protein concentrations, respectively. The osmotic reflection coefficient, an estimation of capillary permeability, was determined by means of the lymph protein wash-down technique. Using the collected data, tissue pressure in the digit was calculated by use of the Starling equation.

In the isolated digit, mean isogravimetric capillary pressure was 55.13 mm of Hg.

Mean plasma and lymph oncotic pressures were 22.29 mm of Hg and 7.2 mm of Hg.

The mean osmotic reflection coefficient was 0.66.

The mean capillary filtration coefficient was 0.003 ml/min/mm of Hg/100 g, and mean interstitial fluid pressure was 44.82 mm of Hg.

The high capillary pressure appeared to be caused by high vascular resistance from the venous side, predisposing to enhanced capillary filtration and interstitial fluid accumulation.”

What is the lymph production rate in these horses?

2. Jane made an appointment with your clinic because her dog has been experiencing breathlessness upon mild exertion. You prescribe a Vo2max test to be done to determine the cause of this exertional dyspnea. On the morning of the test you check your barometer to enter the correct value into your metabolic measurements software, and it read 758 mmHg. When you scheduled Jane’s appointment, you instructed her to feed her dog a protein rich breakfast (R=0.8) in preparation for this Vo2max test. You and your exercise technician assist Jane’s dog onto a treadmill and outfit her with a mask to collect all of her expired gases (the in-line pneumotachograph measures her tidal volume and breathing frequency) and a pulse-oximeter which will measure her heart rate and arterial oxygen saturation (98%). Before beginning the Vo2max test, you establish her normal resting cardio-pulmonary values. You measure her average resting tidal volume to be 100 mL and her breathing frequency to be 30 per minute. The oxygen analyzer readings swing between 0.2095 and 0.1781 as each breath is analyzed, and your administration of a helium dilution test reveals that dead space volume is 30 mL. Your radiologist has set up imaging equipment and is able to visualize blood flow in the heart; he reports that at rest Jane’s dog’s end-diastolic volume is 53 mL and that her end-systolic volume is 6 mL. Corresponding arterial pressure measurements reveal 90 mmHg during diastole and 140 mmHg during systole with a heart rate of 82 beats each minute. Blood tests revealed that her hematocrit levels were 16 g 100mL-1.

– What was Jane’s dog’s venous oxygen content?

Once baseline measurements were recorded, you had the dog begin running. Once she reached Vo2max, your radiologist reported that end-diastolic volume had increased 4-fold, but end-systolic volume had not changed. Jane’s dog’s Vo2max was 1234 mL min-1, and her oxygen extraction doubled.

– How did her cardiac output change to account for this Vo2max? What might be a few of the reasons for Jane’s dog’s exertional dyspnea?

– What else would you want to know to make a diagnosis? You are concerned about Jane’s dog’s high systolic pressure even at rest; what practical advice would you give Jane about reducing her dog’s blood pressure? Why (what are the physics which underlie your reasons)?

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