Hyperdynamic sepsis depresses circulatory compensation to normovolemic anemia in conscious rats

This study was designed to determine whether sepsis modifies the ability to preserve vital organ O2 delivery (QO2) across a clinically relevant range of hematocrits. Ninety rats were randomly allocated to cecal ligation and perforation (CLP) or a sham (Sham) procedure. With the use of rat plasma, rat whole blood, or packed rat red blood cells, respectively, randomization into three different hematocrit subgroups followed: low (21-28%), middle (33-40%), and high (45-52%). Organ blood flow values (Q) were measured by the radioactive microsphere technique, and organ QO2 values were calculated. Twenty-four hours after laparotomy, the hematocrit grouping had not modified the interorgan distribution of Q or QO2 in either the CLP or Sham rats. To characterize overall metabolic O2 reserve, rats were then exposed to hypoxia (inspired O2 fraction, 0.08) for 20 min. Whereas cardiac output increased significantly during hypoxia in all experimental groups, myocardial QO2 failed to increase in the low hematocrit Sham subgroup and fell significantly in both the middle- and low-hematocrit CLP subgroups. There was also a lesser redistribution of QO2 away from the small intestine in the low-hematocrit compared with the high-hematocrit CLP subgroup. We conclude that myocardial QO2 is more effectively maintained in septic hypoxic rats if the hematocrit is maintained at levels =45%.

Blood flow to the trachea and bronchi: the pulmonary contribution

It is generally assumed that when pulmonary vascular pressures are normal the pulmonary contribution to central airway blood flow (Qp) is negligible compared with systemic blood flow (Qs). However, it has been suggested in recent reports that a substantial portion of central airway blood flow is Qp. We have attempted to confirm whether there is a pulmonary contribution to central airway blood flow and to describe how it is anatomically distributed. Measurements of Qp were made using the radioactive microsphere technique in anesthetized ventilated dogs (n = 7) and sheep (n = 6). Qs to the central airways was also measured in another group of sheep (n = 10). At the end of each study, animals were killed and the lungs and trachea were excised. Qp to the upper and lower trachea, mainstem bronchi, and lobar bronchi was calculated, and the relative distribution of Qp and Qs to mucosa, cartilage, and adventitia was determined. Results showed a progressive increase (P < 0.01) in Qp (in ml.min-1 x 100 g-1) from upper trachea to lobar bronchi in both dogs and sheep. Qp and Qs supplied mainly the airway adventitia and the mucosa, respectively. Expressed as a percentage, 89 +/- 4% (SE) of Qp was to the adventitia and 0.1 +/- 0.07% was to the mucosa (P < 0.01), whereas 60 +/- 3.2% of Qs was to the mucosa and 22 +/- 4.6% was to the adventitia. In conclusion, in dogs and sheep there is a pulmonary contribution to central airway blood flow that increases from upper trachea to lobar bronchi and that supplies mainly the peritracheal adventitia.

Chemical regulation of cerebral blood flow in turtles

This study was performed to test the effect of the chemical composition of the blood on cerebral blood flow (CBF) regulation in turtles. The CBF response to increases in arterial PCO2 (PaCO2) (hypercapnia) was measured during normoxia and anoxia in anesthetized freshwater turtles Pseudemys scripta. The radioactive-microsphere technique was used to measure CBF. CBF increased with increases in PaCO2. The sensitivity of the CBF response to hypercapnia (delta CBF/delta PaCO2) was 0.68 ml.min-1.100 g-1. Torr-1 during normoxia. delta CBF/delta PaCO2 increased to 3.44 ml.min-1.100 g-1. Torr-1 during anoxia. The increases in CBF occurred at constant mean arterial blood pressure, which indicates that cerebral vascular resistance decreased. The increased CBF response during asphyxia (hypercapnia-anoxia) could be beneficial for survival during prolonged dives by increasing glucose delivery for brain anaerobic metabolism. In addition, increased CBF could aid in regulating brain acid-base composition by controlling extracellular fluid PCO2.

Splanchnic and systemic hemodynamics in mice using a radioactive microsphere technique

Mice are commonly used for the study of human disease processes. However, techniques for measuring systemic and hepatic blood flow in mice have not been developed. We attempted the conventional technique of radiolabeled microsphere injection into the left ventricle, but difficulties were encountered, including unsuspected ventricular perforation and outflow obstruction in 68% of the animals. We therefore evaluated whether an injection into the carotid artery close to the aortic arch can fulfill the criteria (approximately or greater than 300 microspheres in femoral blood or tissues, adequate mixing of microspheres with blood, and no significant alteration of blood pressure during microsphere injection) required for accurate measurement of systemic and regional hemodynamics. Carotid artery injection resulted in adequate mixing and number of microspheres in tissues in 78 and 91% of the animals, respectively. Portal venous inflow was 1.8 +/- 0.3 ml.min-1.g liver tissue-1 and renal blood flow was 5.1 +/- 0.75 ml.min-1.g tissue-1. Compared per unit weight, these values are quite similar to those reported in rats. Cardiac output was 12.1 +/- 1.2 ml/min and cardiac index was 462 +/- 47 ml.min-1.kg body wt-1. The reliability of cardiac output determination is improved if whole body radioactivity is taken into account. Five of 22 animals had to be excluded because of either a low number of microspheres in tissues or inadequate mixing of microspheres with blood (shown by asymmetrical distribution of microspheres between left and right kidney). With modifications, the radioactive microsphere technique can be adapted to the hemodynamic study of mice.

Total and regional blood flows in vascularized skeletal muscle grafts in rabbits

The transplantation of whole skeletal muscles is a common clinical procedure. Although atypical blood flows have been reported in small free muscle grafts, the blood flow of large neurovascular-intact (NVI) and neurovascular-anastomosed (NVA) grafts have not been measured. Because the maximum specific force (N/cm2) of NVI and NVA grafts is 65% that of control muscles, we hypothesized that total and regional blood flows (ml.min-1.100g-1) of NVI and NVA grafts at rest and during twitch contractions are significantly lower than lower flows of control muscles. In rabbits, blood flows of control rectus femoris (RFM) muscles and NVI and NVA grafts of RFM muscles were measured by the radioactive-microsphere technique. In control muscles, blood flow increased linearly from 6.8 +/- 1 ml.min-1.100 g-1 at rest to 64.4 +/- 7 ml.min-1. 100 g-1 at a stimulation frequency of 3 Hz with no further increase at 4 Hz. Total blood flows in grafts were not different from the control RFM muscle values, except for a higher resting flow in NVA grafts and a lower flow at 3 Hz in NVI grafts. Minor variations in regional flows were observed. We conclude that the operative procedures of grafting and repair of blood vessels affect the vascular bed of muscles minimally, and the deficits observed in grafts do not arise from inadequate perfusion.

Systemic and regional haemodynamic effects of a synthetic atrial natriuretic peptide in conscious rats

1. The effect of the intravenous injection of synthetic atrial natriuretic peptide (ANP, 2 μg) on systemic haemodynamics and blood flow to several organs has been studied in conscious rats by the radioactive microsphere technique. 2. ANP induced a 540% increase in sodium excretion and a 310% increase in urine flow. Mean arterial pressure decreased by 21 mmHg and the peripheral resistances decreased by 26%, without significant changes in cardiac output. 3. Renal blood flow increased by 37.7% and small intestine and portal blood flow increased by 39% and by 28% respectively. No other alterations in organ blood flows were observed. 4. From these data it can be concluded that atrial natriuretic peptide shows acute vascular relaxant properties, which seem to be specific for renal and mesenteric territories.