Effects of acute reduction of cardiac output on the renal circulation of the dog

Impact of positive end-expiratory pressure on renal resistive index in mechanical ventilated patients

PURPOSE

Growing evidence shows the complex interaction between lung and kidney in critically ill patients. The renal resistive index (RRI) is a bedside measurement of the resistance of the renal blood flow and it is correlated with kidney injury. The positive end-expiratory pressure (PEEP) level could affect the resistance of renal blood flow, so we assumed that RRI could help to monitoring the changes in renal hemodynamics at different PEEP levels. Our hypothesis was that the RRI at ICU admission could predict the risk of acute kidney injury in mechanical ventilated critically ill patients.

METHODS

We performed a prospective study including 92 patients requiring mechanical ventilation for ≥ 48 h. A RRI ≥ 0.70, was deemed as pathological. RRI was measured within 24 h from ICU admission while applying 5,10 and 15 cmH2O of PEEP in random order (PEEP trial).

RESULTS

Overall, RRI increased from 0.62 ± 0.09 at PEEP 5 to 0.66 ± 0.09 at PEEP 15 (p < 0.001). The mean RRI value during the PEEP trial was able to predict the occurrence of AKI with AUROC = 0.834 [95%CI 0.742-0.927]. Patients exhibiting a RRI ≥ 0.70 were 17/92(18%) at PEEP 5, 28/92(30%) at PEEP 10, 38/92(41%) at PEEP 15, respectively. Thirty-eight patients (41%) exhibited RRI ≥ 0.70 at least once during the PEEP trial. In these patients, AKI occurred in 55% of the cases, versus 13% remaining patients, p < 0.001.

CONCLUSIONS

RRI seems able to predict the risk of AKI in mechanical ventilated patients; further, RRI values are influenced by the PEEP level applied.

TRIAL REGISTRATION

Clinical gov NCT03969914 Registered 31 May 2019.

Physiological homology between Drosophila melanogaster and vertebrate cardiovascular systems

The physiology of the Drosophila melanogaster cardiovascular system remains poorly characterized compared with its vertebrate counterparts. Basic measures of physiological performance remain unknown. It also is unclear whether subtle physiological defects observed in the human cardiovascular system can be reproduced in D. melanogaster. Here we characterize the cardiovascular physiology of D. melanogaster in its pre-pupal stage by using high-speed dye angiography and optical coherence tomography. The heart has vigorous pulsatile contractions that drive intracardiac, aortic and extracellular-extravascular hemolymph flow. Several physiological measures, including weight-adjusted cardiac output, body-length-adjusted aortic velocities and intracardiac shear forces, are similar to those in the closed vertebrate cardiovascular systems, including that of humans. Extracellular-extravascular flow in the pre-pupal D. melanogaster circulation drives convection-limited fluid transport. To demonstrate homology in heart dysfunction, we showed that, at the pre-pupal stage, a troponin I mutant, held-up2 (hdp2), has impaired systolic and diastolic heart wall velocities. Impaired heart wall velocities occur in the context of a non-dilated phenotype with a mildly depressed fractional shortening. We additionally derive receiver operating characteristic curves showing that heart wall velocity is a potentially powerful discriminator of systolic heart dysfunction. Our results demonstrate physiological homology and support the use of D. melanogaster as an animal model of complex cardiovascular disease.

Inhibition of peripheral vascular compensation after the induction of myocardial ischemia in dogs

The fact that peripheral vascular resistance fails to increase, or does so to only a small degree, thus contributing to hypotension after the onset of myocardial ischemia, has been noted in both clinical and experimental studies. We examined this phenomenon in canine kidney, mesentery, spleen, and skeletal muscle after occlusion via ligation of the circumflex coronary artery. Animals anesthetized with pentobarbital sodium (30 mg/kg, IV) and with intact vagus nerves exhibited reduced cardiac output (CO), maintenance of mean arterial blood pressure (MAP) at or near control levels, and increased total peripheral resistance (TPR). Blood flows to the kidney (RBF) and mesentery (MBF) were decreased resulting in substantial elevations of renal vascular resistance (RVR) and mesenteric vascular resistance (MVR). Blood flow supplied to the hindlimb skeletal muscle (FBF) by the femoral artery did not vary substantially from control levels and, therefore, neither did femoral vascular resistance (FVR). Splenic arterial blood flow (SpBF) was somewhat decreased but splenic vascular resistance (Sp VR) remained un changed. Heart rate exhibited no change from control levels.

When coronary artery ligation was preceded by bilateral cervical vagot omy, CO was decreased as before but MAP exhibited sustained decreases. No change from control values was noted in RBF, FBF, MBF, or SpBF. RVR, MVR, and Sp VR were significantly decreased while FVR remained unchanged. TPR in all cases was increased but not to the same degree as was noted in nonvagotomized animals. Again, no change in heart rate occurred.

Unlike the hemodynamic pattern observed in vagotomized dogs subjectedto the induction of myocardial ischemia, treatment of animals with a cholinergic blocking dose of atropine sulfate (1 mg/kg, IV) before coronary artery occlusion produced maintenance of MAP at or near control levels, lesser and slower reductions of CO and significantly increased TPR. No change was observed in RBF, FBF, MBF, SpBF or in RVR, FVR, MVR, and SpVR. Although there were no changes in heart rate from control levels, these values in atropinized dogs were usually higher than corresponding figures in other series.

When the induction of mild pericardial tamponade was substituted for coronary artery ligation, both vagotomized and non-vagotomized dogs exhibited normal peripheral compensations to the resulting hypotension and CO reduction, i.e., RBF decreased markedly and RVR was substantially increased as was TPR. No change in heart rate occurred.

These results indicate that (1) myocardial ischemia is necessary to trigger the abnormal loss of peripheral vascular compensatory responses; (2) vagal afferent nerves serve a protective function by mediating normal compensatory maneuvers, and (3) an additional mechanism, activated by ischemia but masked by the vagi, may cause inappropriate vasodilation when vagal afferent nerve activity is lost. A model has been constructed that presents a possible mechanism mediating the described phenomena.

Participation of the prostaglandins in the control of renal blood flow during acute reduction of cardiac output in the dog

To determine whether renal prostaglandins participate in the regulation of renal blood flow during acute reduction of cardiac output, cardiac venous return was decreased in 17 anesthetized dogs by inflating a balloon placed in the thoracic inferior vena cava. This maneuver decreased cardiac output from 3.69+/-0.09 liters/min (mean+/-SEM) to 2.15+/-0.19 liters/min (P < 0.01) and the mean arterial blood pressure from 132+/-4 to 111+/-5 mm Hg (P < 0.01) and increased total peripheral vascular resistance from 37.6+/-2.5 to 57.9+/-4.8 arbitrary resistance units (RU) (P < 0.01). In marked contrast, only slight and insignificant decreases in the renal blood flow from 224+/-16 to 203+/-19 ml/min and renal vascular resistance from 0.66+/-0.06 to 0.61+/-0.05 arbitrary resistance units (ru) were observed during inflation of the balloon. Concomitant with these hemodynamic changes, plasma renin activity and plasma norepinephrine concentration increased significantly in both the arterial and renal venous bloods. Plasma concentration of prostaglandin E(2) in renal venous blood increased from 34+/-6 to 129+/-24 pg/ml (P < 0.01). The subsequent administration of indomethacin or meclofenamate had no significant effect on mean arterial pressure, cardiac output, and total peripheral vascular resistance, but reduced renal blood flow from 203+/-19 to 156+/-21 ml/min (P < 0.01) and increased renal vascular resistance from 0.61+/-0.05 to 1.05+/-0.21 ru (P < 0.01). Simultaneously, the plasma concentration of prostaglandin E(2) in renal venous blood fell from 129+/-24 to 19+/-3 pg/ml (P < 0.01). Administration of indomethacin to five dogs without prior obstruction of the inferior vena cava had no effect upon renal blood flow or renal vascular resistance. The results indicate that acute reduction of cardiac output enhances renal renin secretion and the activity of the renal adrenergic nerves as well as renal prostaglandin synthesis without significantly changing renal blood flow or renal vascular resistance. Inhibition of prostaglandin synthesis during acute reduction of cardiac output results in an increased renal vascular resistance and reduced renal blood flow. Accordingly, that data provide evidence that renal prostaglandins counteract in the kidney the vasoconstrictor mechanisms activated during acute reduction of cardiac output.

Renal bloodflow and function in the rabbit after surgical trauma. I. An experimental study

The aim of the present study was to examine the influence of surgical trauma on renal blood flow (RBF) and renal funciotn. The renal vessels were catheterized in lightly anaesthetized rabbits and the dye-dilution technique was used to measure renal blood flow and cardiac output. The renal fraction of the cardiac output (RBF % CO), the total peripherauation of the glomerular and tubular function was made by measuring the extraction of EDTA and of Hippuran. A decrease in the cardiac output was accompanied by a diminution of renal blood flow. Renal blood flow was reduced, regardless of whether surgery or puncture of the kidney was performed, probably due to vasoconstriction in the kidney caused by an increase in sympathetic tonus or in the concentration of plasma catecholamines. Manipulation of the renal artery seemed to stimulate further vasoconstriction in the ipsilateral kidney by a direct effect. The glomerular and tubular function decreased initially, independently of surgical trauma, and it is therefore assumed that the initial renal vasoconstriction includes the afferent arterioles. Renal function was not greatly influenced by handling of the renal artery.

Renal blood flow and function in the rabbit after surgical trauma. III. Effects of temporary occlusion of renal artery

The renal artery was occluded in rabbits for varying lengths of time with the aid of a balloon catheter. Before and after the period of ischaemia, renal blood flow was measured by a dye-dilution technique and the glomerular and tubular functions were evaluated by measuring the extractions of labelled EDTA and Hippuran. Prolongation of the period of continuous ischaemia from 15 to 60 minutes resulted in a progressive increase in the postocclusive hyperaemia, but in a reduction of the renal function. Compared with 30 minutes of continuous occlusion, 30 minutes of intermittent occlusion caused only slight hyperaemia, but the same degree of reduction in renal function. One day after 30 minutes or 60 minutes of ischaemia, renal blood flow was within the range of the normal flow. After 30 minutes of occlusion, renal function was re-established 7 days later, whereas after 60 minutes of ischaemia, function was still severely impaired 7 days later. Fourteen days after 60 minutes of occlusion, renal function was 50% or less of the normal. Juxtamedullary shunting has not been demonstrated in the present investigation. Metabolic changes and cellular damage remain as possible explanations of the postocclusive changes in renal blood flow and function.

Renal blood flow and function in the rabbit after surgical trauma. II. The role of constriction in the main renal artery and activation of the alpha-adrenergic receptors

The impairment of renal circulation and function in connection with general anaesthesia and surgical trauma was investigated in 19 rabbits. The systemic circulation and the renal circulation were evaluated by a dye-dilution technique and glomerular and tubular function by measuring the extraction of 51-Cr-EDTA and 125-I-Hippuran. In Group I measurements were performed before and after manipulation of the left renal artery preceded by topical application of a local anaesthetic. In Groups II and III measurements were performed before and after i.v. injection of, respectively, 0.8 and 3.0 mg/kg body-weight phenoxybenzamine, and then after manipulation of the renal artery. Blockade of the alpha-adrenergic receptors with phenoxybenzamine was found to preserve the renal fraction of the cardiac output. The blockade prevented an initial reduction in the extraction of EDTA and Hippuran, previously ascribed to general anaesthesia, but did not prevent a diminution following surgical handling of the kidney and the renal artery. The local anaesthesia had no effect. It is concluded that general anaesthesia and surgical trauma cause an impairment of the renal circulation due to an increased concentration of plasma catecholamines.

Studies on the renal circulation and renal function in mitral valvular disease. I. Effect of exercise

In 31 patients with mitral stenosis of varying severity the effect of light, steady exercise during 15 to 17 minutes on renal function and renal circulation has been studied during heart catheterization. The results have been compared with the values obtained at rest in 72 patients with mitral stenosis. Exercise produced a decrease in clearance of para-aminohippurate and sodium excretion and an increase in renal resistance, changes not produced in normal individuals. Cardiac output and pulmonary pressures increased. In patients with right heart failure exercise produced increased pressures but no increase in cardiac output, and only slight changes in clearance but increase in renal resistance and renal venous pressure.