Effect of Hematocrit and Inertial Losses on Pressure-Flow Relations in the Isolated Hindpaw of the Dog

Abstract

The effect of hematocrit on pressure-flow relations was studied in the perfused isolated hindpaw of the dog. Blood and suspensions of erythrocytes (RBC) in albumin-Ringer solution, hematocrit range of 0 to 80%, were used as perfusates. Flow resistance was found to increase markedly with hematocrit. No significant difference was found between pressure-flow data obtained with blood and RBC in albumin-Ringer solution when comparisons were made at comparable hematocrits, indicating negligible effect of RBC aggregation when blood was the perfusion fluid. Computations of flow resistance relative to cellfree perfusate indicated that non-Newtonian viscosity, as well as vessel distensibility, contributed to the nonlinearity of pressure-flow curves. Perfusion of paws with two Newtonian fluids of different viscosities allowed computation of inertial pressure losses under conditions of steady flow. At physiological perfusion pressures, inertial losses accounted for about 40% of the total pressure drop for cell-free albumin-Ringer solution, and dropped to about 5% for a hematocrit of 50. The results suggest that inertial losses, rather than a Fahraeus-Lindqvist effect, play an important role in pressure-flow relations in the hindpaw. 1047 at UNIV OF NORTH DAKOTA on May 15, 2015 http://circres.ahajournals.org/ Downloaded from 1048 BENIS, USAMI, CHIEN pressure-flow relations. The results do not support the existence of a Fahraeus-Lindqvist effect in the perfused hindpaw. Methods PERFUSIONS WITH RBC SUSPENSIONS AT DIFFERENT HEMATOCRITS Colled.d Blood Weight FIGURE 1 (A) Schematic drawing of perfusion circuit. Cannulated paw on balance is perfused by dog's natural blood (connections to femoral artery and vein) or by syringe pump. Inset shows cannula manifolds.(B) Variables displayed on multichannel recorder include venous pressure (P T ), arterial pressure (P 8 ), paw weight (W p ) and weight of collected fluid (W q ).

Primary Pulmonary Hypertension with Severe Systemic Hypertension, Raynaud's Phenomenon and Relative Polycythemia.

“…Roos calculated that pulmonary perfusion pressure increases three-fold when the blood hematocrit is raised from 40%to 80% (5). Benis and associates found that pulmonary resistance increases three-fold when the hematocrit is increased from 42%to 80%in perfused canine hindpaws (6). Thus in the present case, the increase in hematocrit is likely related in part to systemic hypertension and pulmonary hypertension.…”

Cerebral Blood Flow, Oxygen, Carbon Dioxide Tensions, and Blood Bicarbonate in Controlling Drive and Timing in Patients with Chronic Obstructive Pulmonary Diseases

“…These flow changes are not primarily caused by cerebrovascular con trol mechanisms, but rather by alterations in blood viscosity [13,14], Proper breathing, which involves both drive and timing, is achieved through a series of complicated feedback mechan isms. When there is disturbance in the function of this respiratory feedback sys tem, blood flow and more especially re gional CBF may contribute to delay in in formation transfer.…”

Report of the Hypertension Task Force of the National Heart, Lung, and Blood Institute. Current research and recommendations from the Subgroup on Local Hemodynamics.

“…** 4 Within the past 2 years, however, there have been reports of elevations in pulmonary artery pressure and resistance at rest in some patients with established essential hypertension, in the absence of increases in pulmonary capillary wedge pressure or any evidence for left ventricular failure. 3 "' 358 The patients, however, did have left ventricular hypertrophy, so there remains the possibility that the increased pulmonary pressures and resistances represented residual effects of the elevated left heart filling pressures that probably occurred with activity in these patients. Similar studies in patients with mild uncomplicated or borderline hypertension would help to better assess effects of left ventricular dysfunction.…”

“…Most of these studies were made a number of years ago and reported normal pulmonary hemodynamics in hypertensive patients at rest, 3 "" 3 " with the exception of elevations accompanying left ventricular dysfunction. 1 " It was also known that with exercise, pressures and resistances in the pulmonary circuit in hypertensives became abnormally high, accompanied by abnormal elevations of pulmonary capillary wedge pressures.…”

“…Evidence based on micropuncture of distal tubules in Munich Wistar rats with surface glomeruli indicates that autoregulation of the nephron glomerular filtration rate is impaired in the untouched kidney in rats with twokidney, one clip hypertension. 1 * 3 The mechanism may involve reduced efficiency of a tubuloglomerular feedback loop involving the renin-angiotensin system. Unfortunately, SHR do not possess surface glomeruli.…”