Intraoperative administration of inhaled carbon monoxide reduces delayed graft function in kidney allografts in Swine.

Ischemia/reperfusion injury and delayed graft function (DGF) following organ transplantation adversely affect graft function and survival. A large animal model has not been characterized. We developed a pig kidney allograft model of DGF and evaluated the cytoprotective effects of inhaled carbon monoxide (CO). We demonstrate that donor warm ischemia time is a critical determinant of DGF as evidenced by a transient (4-6 days) increase in serum creatinine and blood urea nitrogen following transplantation before returning to baseline. CO administered to recipients intraoperatively for 1 h restored kidney function more rapidly versus air-treated controls. CO reduced acute tubular necrosis, apoptosis, tissue factor expression and P-selectin expression and enhanced proliferative repair as measured by phosphorylation of retinol binding protein and histone H3. Gene microarray analyses with confirmatory PCR of biopsy specimens showed that CO blocked proinflammatory gene expression of MCP-1 and heat shock proteins. In vitro in pig renal epithelial cells, CO blocks anoxia-reoxygenation-induced cell death while promoting proliferation. This large animal model of DGF can be utilized for testing therapeutic strategies to reduce or prevent DGF in humans. The efficacy of CO on improving graft function posttransplant validates the model and offers a potentially important therapeutic strategy to improve transplant outcomes.

Inhaled nitric oxide delivery and monitoring.

Inhaled nitric oxide (NO) was found to cause selective pulmonary vasodilation in the late 1980's and since then there has been a huge interest in studying its clinical benefits. The equipment used to deliver and monitor inhaled NO has gone through a dramatic evolution from simple flow meters and industrial monitors to to-days purpose built, fully integrated, NO delivery and monitoring systems that were designed specifically for the demanding area of the intensive care unit. This paper explores the evolution of inhaled NO delivery systems and identifies the design challenges, the safety and regulatory requirements and the ease of use issues that had to be solved to bring this new exciting new class of medical device in to clinical use.

The effects of carotid body hypocapnia on ventilation in goats.

This study was designed to examine the influence of carotid body (CB) hypocapnia on ventilation by selectively perfusing the CB through an extracorporeal circuit in 19 goats. When PcbCO2 was decreased from normocapnic levels in 14 awake goats (delta PcbCO2 = 10.9 Torr), PaCO2 increased 5.6 Torr (P less than 0.05) and VE decreased 24% (P less than 0.001) (mean values). The ventilatory sensitivity to inspired CO2 was not changed by CB hypocapnia in 5 of these goats, but the response was shifted to the right. During CB hypocapnia, ventilatory instability, including apnea, was observed in 4 of 14 goats; this irregular breathing continued at elevated levels of PaCO2. In 5 anesthetized goats, CB hypocapnia (delta PcbCO2 = 18.0 Torr) decreased VE by 70% in the intact state, but produced no significant ventilatory depression after CB denervation. We conclude that CB hypocapnia depresses ventilation in both awake and anesthetized goats mostly through CB chemoreceptor effects, and suggest that this hypoventilation may predispose to ventilatory instability in some animals.

Hypoxic-hypercapnic ventilatory interaction at the carotid body of awake goats.

Neurophysiological studies have demonstrated that a positive interaction between hypoxic and hypercapnic stimuli occurs at the carotid body (CB). The present study was designed to confirm that this interaction at the CB was translated into a similar interaction in the ventilatory response. By utilizing an awake goat model in which the CB could be selectively perfused using an extracorporeal circuit we avoided confounding central effects. In six goats the CB was stimulated by progressively decreasing PcbO2 from 160 to 40 Torr at two constant levels of PcbCO2, 36 and 61 Torr. The animals breathed room air with supplemental CO2 to maintain systemic isocapnia. The response to CB hypoxia was significantly greater in CB hypercapnia than in CB normocapnia for minute ventilation, tidal volume, respiratory frequency, and mean inspiratory flow rate. We conclude that the hypercapnic-hypoxic interaction at the CB is reflected in the ventilatory responses of the animal.

Carotid body hypercapnia does not elicit ventilatory acclimatization in goats.

The carotid body (CB) perfusion model utilizes surgical vascular ligations to allow isolated blood supply to a single in situ CB in awake goats. The contralateral CB was excised. By use of an extracorporeal pump-oxygenator system the blood gas composition perfusing the CB can be controlled independently from that of the systemic arterial system including the brain. Using this model we compared the responses of systemically normoxic goats to CB hypercapnia and CB hypoxia. In 6 goats CB stimulation with hypercapnic-normoxic blood (mean PcbCO2 = 78 Torr, mean PcbO2 congruent to 100 Torr) produced acute hyperventilation (mean decrease in PaCO2 of 5.2 Torr, P less than 0.05) which remained constant over the 4-h perfusion period. Lack of a progressively increasing hyperventilation indicates that ventilatory acclimatization did not occur with hypercapnic CB perfusion. Hypoxic-normocapnic CB stimulation (mean PcbO2 = 40 Torr, mean PcbCO2 = 39 Torr) produced an acute mean decrease in PaCO2 of 5.5 Torr (P less than 0.05) in 6 additional goats. In contrast to CB hypercapnia, the acute hyperventilation induced by CB hypoxia was followed by a progressive time-dependent additional mean decrease in PaCO2 of 5.6 Torr (P less than 0.05) over a 4-h period (ventilatory acclimatization). These data are compatible with the concept of separate receptor mechanisms for hypercapnia and hypoxia in the CB and suggest that the early phase of ventilatory acclimatization to hypoxia in goats may result from a time-dependent increase in CB afferent output.

Effects of sleep state on ventilatory acclimatization to hypoxia in humans.

We assessed the influence of sleep state on ventilatory acclimatization to hypoxia. Ventilation, arterial O2 saturation (SaO2), and arterial acid-base status were monitored in healthy adult males during wakefulness, nonrapid-eye-movement (NREM) sleep, and rapid-eye-movement (REM) sleep in normoxia [barometric pressure (PB) = 740 Torr] and over 4 continuous days of hypobaric hypoxia (PB = 455 Torr). The relative hypoventilation observed during sleep compared with wakefulness in normoxia was also observed during all stages of hypoxic acclimatization. The characteristic time-dependent changes associated with acclimatization to chronic hypoxia were similar during wakefulness and all sleep states: 1) arterial CO2 partial pressure (PaCO2) decreased 27-31% by night 4 with approximately half of this fall occurring acutely (0.3-3 h hypoxia); 2) minute ventilation increased progressively with duration of hypoxic exposure including increased levels of hyperventilation throughout the initial night of sleep in hypoxia; 3) SaO2 was lowest acutely and gradually increased coincident with the progressive hyperventilation; and 4) pHa increased acutely and remained unchanged despite additional hyperventilation due to a compensatory reduction in [HCO3-]a. In addition, in the acclimatized subject hyperventilation persisted following acute restoration of normoxia, and this continued hyperventilation was similar in magnitude during both wakefulness and NREM sleep. These results indicate that suprapontine influences on ventilatory control associated with the state of wakefulness are not required in the process of ventilatory acclimatization to chronic hypoxia.

Mechanisms of hypoxia-induced periodic breathing during sleep in humans.

Ventilation was studied during wakefulness and sleep in six healthy humans in normoxia (mean barometric pressure (PB) = 740 torr), and in hypobaric hypoxia (PB = 455 torr). Hypoxia caused hyperventilation and hypocapnic alkalosis (delta Pa,CO2 = -7 torr) during wakefulness and in all sleep states. Periodic breathing was the predominant pattern of breathing in all stages of non-rapid eye movement (non-r.e.m.) sleep in hypoxia, but was rarely observed during wakefulness or r.e.m. sleep. Periodic breathing was composed of repetitive oscillations of reproducible cycle length characterized by clusters of breaths with augmented inspiratory effort (VT/TI) and highly variable distribution of breath-to-breath minute ventilation (VE) and tidal volume (VT), which alternated regularly with prolongations of the expiratory pause of the last breath of each cluster (apnea duration = 5-18 sec). Hypoxia-induced periodic breathing was eliminated by: (a) acute restoration of normoxia coincident with a 3-6 torr increase in Pa,CO2; and (b) augmented FI,CO2 (at constant arterial oxygen saturation) which rapidly and reversibly eliminated apneas and stabilized breathing pattern with a less than 2 torr increase in Pa,CO2. If hypocapnia was prevented (by augmented FI,CO2) during acute induction of hypoxia in non-r.e.m. sleep, periodic breathing was also prevented. We propose that the genesis of hypoxia-induced periodic breathing requires the combination of hypoxia and hypocapnia. Periodicity results from oscillations in CO2 about a CO2-apnea threshold whose functional expression is critically linked to sleep state.

Ventilatory adaptations to resistive loading during wakefulness and non-REM sleep.

Ventilatory and timing responses to repetitive and sustained inspiratory resistive loading were assessed in six naive male subjects during wakefulness (AW) and non-REM sleep (NREM). In five of six subjects, tidal volume (VT) was maintained or increased with repetitive five-breath loading periods during wakefulness. In these five subjects, mouth occlusion pressure (P100) increased with loading during AW (1.8 +/- 0.5 control vs. 2.2 +/- 0.4 cmH2O loaded, P less than 0.05), but not during NREM (2.1 +/- 1.5 control vs. 2.1 + 1.5 cmH2O loaded). For each state, VT and frequency (f) responses to sustained loads were similar to responses to five-breath loads. During sustained loading; a) VT increased 35% during AW, decreased 28% during NREM, b) f decreased 35% during AW, increased 6% during NREM, c) minute ventilation (VE) decreased 12% during AW, decreased 23% during NREM. Ventilatory responses persisted until arousal (0.4--1.7 min) in NREM. With repetitive loading: a) inspiratory duration (TI) increased during AW but did not change during NREM, b) "duty cycle" (TI/TT) increased with loading in both states. These findings suggest that a) NREM abolishes between-breath augmentations in P100, b) within-breath load compensation is operant during both AW (preserved VT) and NREM (failure of predicted TI prolongation) by differing mechanisms, c) arousal may be a ventilatory compensation to inspiratory resistive loading in NREM.

Correction of CO2 retention during sleep in patients with chronic obstructive pulmonary diseases.

Three normal subjects and 5 patients with chronic obstructive pulmonary disease and chronic CO2 retention were studied to determine the effect of chronic ventilatory stimulation with medroxyprogesterone acetate (MPA) on ventilatory control and pulmonary gas exchange during sleep. All patients had lowered PaCO2 after treatment with MPA while awake. Using a randomized application of treatment and placebo conditions, 4 wk of MPA therapy in the normal subjects caused a reduction in PaCO2 while awake (delta PaCO2 -4 to -7 mmHg) and during non-REM sleep (delta PaCO2 -5 to -7 mmHg). The response consisted of an increased minute ventilation (VE), tidal volume (VT), and mean inspiratory flow (VT/TI) awake and during non-REM sleep. In the patient group, 4 wk of MPA therapy caused significant reductions in PaCO2 while awake (from 54 +/- 2 to 47 +/- 2 mmHg) and during non-REM sleep (from 57 +/- 2 to 49 +/- 2 mmHg). Minute ventilation tidal volume, and mean inspiratory flow increased to a similar extent while awake and during all sleep stages. Improvement in SaO2 during sleep induced by treatment was attributable to an increase in alveolar ventilation rather than a decrease in alveolar-arterial oxygen partial pressure difference. Medroxyprogesterone acetate elicited chronic increases in inspiratory effect, tidal volume, and alveolar ventilation while awake and during all sleep stages in selected patients with chronic CO2 retention despite severe mechanical impairment and maldistribution ventilation:perfusion. The drug drives ventilation by a mechanism of action that is independent of many other peripheral and "central" ventilatory stimuli and/or inhibitors, including higher central nervous system influenced on ventilatory control that are dependent on the state of wakefulness.

The effect of pregnancy on the angiotensin II pressor response in the rabbit.

The pressor response to angiotensin II was measured in unanesthetized, chronically catheterized pregnant and nonpregnant rabbits. Angiotensin II was infused intravenously for 10 minutes at a dose of 50 and 124 ng/kg/min. No difference in control mean arterial blood pressure was observed between pregnant and nonpregnant rabbits. The pressure change in response to angiotensin II was significantly greater in nonpregnant rabbits than in pregnant rabbits (P less than 0.002). Plasma samples were analyzed for angiotensin II concentration by radioimmunoassay. The results showed that there was no difference in plasma angiotensin II concentration between pregnant and nonpregnant rabbits following angiotensin II infusions. In a separate series we observed the effect of 5 mg of phenoxybenzamine on the pressor response to angiotensin II. After phenoxybenzamine treatment the control mean arterial blood pressure was significantly greater in nonpregnant rabbits than in pregnant rabbits, but the change in pressure in response to angiotensin II in nonpregnant rabbits was not significantly different from that of pregnant rabbits. These results show (1) that pregnant rabbits have a decreased sensitivity to angiotensin II, (2) that this decreased sensitivity is not due to differences in plasma concentration of angiotensin II, and (3) that this differential sensitivity to angiotensin II can be prevented by alpha-receptor blockade.

Effect of prostaglandin I2 on ovine placental vasculature.

The response of the placental circulations to prostaglandin I2 (maternal dose 20 microgram/kg, fetal dose 180 microgram/kg) was observed in 10 near-term sheep with chronically implanted vascular catheters. The blood flows before and 90 s after the injection of prostaglandin I2 were measured using radioactive microspheres. The injection of prostaglandin I2 to the mother decreased th blood pressure from 109 +/- 4 to 69 +/- 5 mmHg (P < 0.001) and increased the vascular resistance of the maternal cotyledons from 0.166 +/- 0.018 to 0.209 +/- 0.02 mmHg/(ml/min) (P < 0.001). The vascular bed of the non-cotyledonary uterus vasodilated as the resistance fell from 0.705 +/- 0.02 to 0.266 +/- 0.02 mmHg/(ml/min). (P < 0.001). Prostaglandin I2 caused the fetal arteriovenous pressure to fall from 37.6 +/- 1.35 to 26.0 +/- 1.6 mmHg. There was no significant change in the vascular resistance of the fetal cotyledons. We observed vasodilation in the fetal membranes as vascular resistance fell from 1.06 +/- 0.14 to 0.75 +/- 0.10 mmHg/(ml/min) (P < 0.001). The infusion of prostaglandin I2 significantly depressed the response of the placenta and uterus to norepinephrine. We have not proved that prostaglandin I2 plays a direct role in maintaining placental vascular homeostasis but it may modulate the response of this organ to exogenous vasoactive agents.

Ovine placental vascular responses to indomethacin.

The administration of 10 mg/kg indomethacin to chronically catheterized near-term sheep resulted in a change in cotyledonary vascular resistance from 0.133 +/- 0.016 to 0.180 +/- 0.022 (mmHg . min)/ml (P less than 0.001). The noncotyledonary uterine vascular resistance increased to 191% of the original value (P less than 0.001) and the renal vascular resistance increased to 147% of the control value (P less than 0.001). The maternal blood pressure increased from 96 +/- 3.4 to 108 +/- 3.4 mmHg (P less than 0.001). Indomethacin (12 mg/kg) was given to nine fetuses, and observations were made in the control condition and at 15, 120, and 240 min. Cotyledonary vascular resistances were 144%, 152%, and 213% of the control values at those times. All changes were significant (P less than 0.03). The umbilical vascular resistance rose slowly throughout the study even though the concentration of indomethacin was falling during that time. These data suggest that this response may be an indirect effect. In the maternal circulation the rapid increase in the cotyledonary vascular resistance seen after indomethacin was probably due to a decreased level of endogenous prostaglandin synthesis.