Inhaled nitric oxide for the adult respiratory distress syndrome

BACKGROUND

The adult respiratory distress syndrome is characterized by pulmonary hypertension and right-to-left shunting of venous blood. We investigated whether inhaling nitric oxide gas would cause selective vasodilation of ventilated lung regions, thereby reducing pulmonary hypertension and improving gas exchange.

METHODS

Nine of 10 consecutive patients with severe adult respiratory distress syndrome inhaled nitric oxide in two concentrations for 40 minutes each. Hemodynamic variables, gas exchange, and ventilation-perfusion distributions were measured by means of multiple inert-gas-elimination techniques during nitric oxide inhalation; the results were compared with those obtained during intravenous infusion of prostacyclin. Seven patients were treated with continuous inhalation of nitric oxide in a concentration of 5 to 20 parts per million (ppm) for 3 to 53 days.

RESULTS

Inhalation of nitric oxide in a concentration of 18 ppm reduced the mean (+/- SE) pulmonary-artery pressure from 37 +/- 3 mm Hg to 30 +/- 2 mm Hg (P = 0.008) and decreased intrapulmonary shunting from 36 +/- 5 percent to 31 +/- 5 percent (P = 0.028). The ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2), an index of the efficiency of arterial oxygenation, increased during nitric oxide administration from 152 +/- 15 mm Hg to 199 +/- 23 mm Hg (P = 0.008), although the mean arterial pressure and cardiac output were unchanged. Infusion of prostacyclin reduced pulmonary-artery pressure but increased intrapulmonary shunting and reduced the PaO2/FiO2 and systemic arterial pressure. Continuous nitric oxide inhalation consistently lowered the pulmonary-artery pressure and augmented the PaO2/FiO2 for 3 to 53 days.

CONCLUSIONS

Inhalation of nitric oxide by patients with severe adult respiratory distress syndrome reduces the pulmonary-artery pressure and increases arterial oxygenation by improving the matching of ventilation with perfusion, without producing systemic vasodilation. Randomized, blinded trials will be required to determine whether inhaled nitric oxide will improve outcome.

Inhaled prostacyclin and iloprost in severe pulmonary hypertension secondary to lung fibrosis

Pulmonary hypertension is a life-threatening complication of lung fibrosis. Vasodilator therapy is difficult owing to systemic side effects and pulmonary ventilation-perfusion mismatch. We compared the effects of intravenous prostacyclin and inhaled NO and aerosolized prostacyclin in randomized order and, in addition, tested for effects of oxygen and systemic calcium antagonists (CAAs) in eight patients with lung fibrosis and pulmonary hypertension. Aerosolized prostaglandin (PG)I(2) caused preferential pulmonary vasodilatation with a decrease in mean pulmonary arterial pressure from 44.1 +/- 4.2 to 31.6 +/- 3.1 mm Hg, and pulmonary vascular resistance (RL) from 810 +/- 226 to 386 +/- 69 dyn. s. cm(-)(5) (p < 0.05, respectively). Systemic arterial pressure, arterial oxygen saturation, and pulmonary right-to-left shunt flow, measured by multiple inert gas analysis, were not significantly changed. Inhaled NO similarly resulted in selective pulmonary vasodilatation, with RL decreasing from 726 +/- 217 to 458 +/- 81 dyn. s. cm(-)(5). In contrast, both intravenous PGI(2) and CAAs were not pulmonary selective, resulting in a significant drop in arterial pressure. In addition, PGI(2) infusion caused a marked increase in shunt flow. Long-term therapy with aerosolized iloprost (long-acting PGI(2) analog) resulted in unequivocal clinical improvement from a state of immobilization and severe resting dyspnea in a patient with decompensated right heart failure. We concluded that, in pulmonary hypertension secondary to lung fibrosis, aerosolization of PGI(2) or iloprost causes marked pulmonary vasodilatation with maintenance of gas exchange and systemic arterial pressure. Long-term therapy with inhaled iloprost may be life saving in decompensated right heart failure from pulmonary hypertension secondary to lung fibrosis.

Worsening of pulmonary gas exchange with nitric oxide inhalation in chronic obstructive pulmonary disease

BACKGROUND

Inhalation of nitric oxide (NO) causes selective pulmonary vasodilation and improves arterial oxygenation in acute respiratory distress syndrome. But some patients do not respond or gas exchange worsens when inhaling NO. We hypothesised that this detrimental effect might be related to the reversion of hypoxic vasoconstriction in those patients where this mechanism contributes to ventilation-perfusion (V(A)/Q) matching.

METHODS

We studied 13 patients with advanced chronic obstructive pulmonary disease (COPD). We compared their responses to breathing room air, NO at 40 parts per million in air, and 100% O2. Changes in pulmonary haemodynamics, blood gases, and V(A)/Q distributions were assessed.

FINDINGS

NO inhalation decreased the mean (SE) pulmonary artery pressure from 25.9 (2.0) to 21.5 (1.7) mm Hg (p = 0.001) and PaO2 from 56 (2) 53 (2) mm Hg (p = 0.014). The decrease in PaO2 resulted from worsening of V(A)/Q distributions, as shown by a greater dispersion of the blood-flow distribution (logSD Q) from 1.11 (0.1) to 1.22 (0.1) (p = 0.018). O2 breathing reduced the mean pulmonary arterial pressure to 23.4 (2.1) mm Hg and caused greater V(A)/Q mismatch (logSD Q, 1.49 [0.1]). The intrapulmonary shunt on room air was small (2.7 [0.9]%) and did not change when breathing NO or O2.

INTERPRETATION

We conclude that in patients with COPD, in whom hypoxaemia is caused essentially by V(A)/Q imbalance rather than by shunt, inhaled NO can worsen gas exchange because of impaired hypoxic regulation of the matching between ventilation and perfusion.

Performance and metabolic responses to a high caffeine dose during prolonged exercise

The present study examined whether a high caffeine dose improved running and cycling performance and altered substrate metabolism in well-trained runners. Seven trained competitive runners [maximal O2 uptake (VO2max) 72.6 +/- 1.5 ml.kg-1.min-1] completed four randomized and double-blind exercise trials at approximately 85% VO2max; two trials running to exhaustion and two trials cycling to exhaustion. Subjects ingested either placebo (PL, 9 mg/kg dextrose) or caffeine (CAF, 9 mg/kg) 1 h before exercise. Endurance times were increased (P less than 0.05) after CAF ingestion during running (PL 49.2 +/- 7.2 min, CAF 71.0 +/- 11.0 min) and cycling (PL 39.2 +/- 6.5 min, CAF 59.3 +/- 9.9 min). Plasma epinephrine concentration [EPI] was increased (P less than 0.05) with CAF before running (0.22 +/- 0.02 vs. 0.44 +/- 0.08 nM) and cycling (0.31 +/- 0.06 vs. 0.45 +/- 0.06 nM). CAF ingestion also increased [EPI] (P less than 0.05) during exercise; PL and CAF values at 15 min were 1.23 +/- 0.13 and 2.51 +/- 0.33 nM for running and 1.24 +/- 0.24 and 2.53 +/- 0.32 nM for cycling. Similar results were obtained at exhaustion. Plasma norepinephrine was unaffected by CAF at rest and during exercise. CAF ingestion also had no effect on respiratory exchange ratio or plasma free fatty acid data at rest or during exercise. Plasma glycerol was elevated (P less than 0.05) by CAF before exercise and at 15 min and exhaustion during running but only at exhaustion during cycling. Urinary [CAF] increased to 8.7 +/- 1.2 and 10.0 +/- 0.8 micrograms/ml after the running and cycling trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous nitric oxide as a probable modulator of pulmonary circulation and hypoxic pressor response in vivo

The objective of this study was to investigate the role of endogenous nitric oxide, formed from L-arginine, in the regulation of pulmonary circulation in vivo, with special reference to the hypoxic pressor response. In artificially ventilated open-chest rabbits, pulmonary vascular resistance at normoxic ventilation (FIO2 = 21%) was 78 +/- 16 cmH2O ml-1 min 1000-1 (mRUL). Hypoxic ventilation (FIO2 = 10%) increased pulmonary vascular resistance to 117 +/- 17 mRUL. N omega-nitro-L-arginine methylester (L-NAME), an inhibitor of nitric oxide synthase, increased pulmonary vascular resistance at normoxic ventilation to 192 +/- 28 mRUL and during hypoxic ventilation to 462 +/- 80 mRUL. During N omega-nitro-L-arginine methylester infusion there was also an increase in mean arterial blood pressure as well as a decrease in cardiac output that was even more pronounced during hypoxic ventilation. L-arginine reversed the effect of N omega-nitro-L-arginine methylester on pulmonary vascular resistance at normoxic ventilation to 140 +/- 26 mRUL and at hypoxic ventilation to 239 +/- 42 mRUL. In spontaneously breathing closed-chest rabbits, N omega-nitro-L-arginine methylester evoked a marked decrease in arterial PO2 and increases in respiration frequency and central venous pressure, while blood pH, PCO2 and base excess remained unchanged. Taken together these findings indicate that endogenous nitric oxide, formed from L-arginine, might be a regulator of ventilation-perfusion matching at normoxic ventilation, and that nitric oxide acts as an endogenous modulator of the hypoxic pressor response.

Prostaglandin E1 and nitroglycerin reduce pulmonary capillary pressure but worsen ventilation-perfusion distributions in patients with adult respiratory distress syndrome

Pulmonary artery hypertension associated with adult respiratory distress syndrome (ARDS) may increase microvascular filtration pressure by increasing pulmonary capillary pressure (PCP). To evaluate the potential to reverse this consequence of pulmonary artery hypertension, the effects of short-term vasodilator treatment were compared with prostaglandin E1 (PGE1) or nitroglycerin (NTG) on pulmonary hemodynamics and gas exchange. The two vasodilators were infused in ten patients with mild or moderate ARDS at a dosage rate achieving a 20% reduction of the mean arterial pressure. PCP was estimated by graphic analysis of the pulmonary artery occlusion curve, and continuous ventilation-perfusion (VA/Q) distributions were assessed using the multiple inert gas technique. At the given dosages both drugs induced equivalent reductions of the mean pulmonary artery pressure (PAP) from 28.2 +/- 3.6 to 23.7 +/- 3.2 with PGE1 and to 23.4 +/- 3.2 mmHg with NTG. The right atrial and pulmonary artery wedge pressure (PAWP) were also decreased to the same extent associated with the expected decrease in PCP from 17.4 +/- 2.6 to 15.1 +/- 3.3 with PGE1 and to 15.6 +/- 2.7 mmHg with NTG. The estimated PCP values were closely correlated with the values calculated according to Gaar's equation (r = 0.822. n = 23, P less than 0.001) with a regression close to the identity line. The contribution of pulmonary venous resistances to the resistance of the whole pulmonary vascular bed computed as the ratio (PCP- PAWP)/(PAP-PAWP) was 0.28 and remained unchanged during vasodilator infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhaled prostacyclin is safe, effective, and affordable in patients with pulmonary hypertension, right heart dysfunction, and refractory hypoxemia after cardiothoracic surgery

BACKGROUND

The purpose of this study was to describe our institutional experience in using inhaled prostacyclin as a selective pulmonary vasodilator in patients with pulmonary hypertension, refractory hypoxemia, and right heart dysfunction after cardiothoracic surgery.

METHODS

Between February 2001 and March 2003, cardiothoracic surgical patients with pulmonary hypertension (mean pulmonary artery pressure >30 mm Hg or systolic pulmonary artery pressure >40 mm Hg), hypoxemia (PaO(2)/fraction of inspired oxygen <150 mm Hg), or right heart dysfunction (central venous pressure >16 mm Hg and cardiac index <2.2 L.min(-1).m(-2)) were prospectively administered inhaled prostacyclin at an initial concentration of 20,000 ng/mL and then weaned per protocol. Hemodynamic variables were measured before the initiation of inhaled prostacyclin, 30 to 60 minutes after initiation, and again 4 to 6 hours later.

RESULTS

One hundred twenty-six patients were enrolled during the study period. At both time points, inhaled prostacyclin significantly decreased the mean pulmonary artery pressure without altering the mean arterial pressure. The average length of time on inhaled prostacyclin was 45.6 hours. There were no adverse events attributable to inhaled prostacyclin. The average cost for inhaled prostacyclin was 150 US dollars per day. Compared with nitric oxide, which costs 3000 US dollars per day, the potential cost savings over this period were 681,686 US dollars.

CONCLUSIONS

Inhaled prostacyclin seems to be a safe and effective pulmonary vasodilator for cardiothoracic surgical patients with pulmonary hypertension, refractory hypoxemia, or right heart dysfunction. Overall, inhaled prostacyclin significantly decreases mean pulmonary artery pressures without altering the mean arterial pressure. Compared with nitric oxide, there is no special equipment required for administration or toxicity monitoring, and the cost savings are substantial.

Pulmonary ventilation/perfusion defects induced by epinephrine during cardiopulmonary resuscitation

BACKGROUND

Epinephrine has been shown to impair pulmonary excretion of CO2 during resuscitation. This phenomenon was investigated in a rodent model of cardiac arrest and conventional resuscitation.

METHODS AND RESULTS

The effects of racemic epinephrine were compared with the selective alpha 1-agonist methoxamine and with saline placebo during cardiac resuscitation in 15 Sprague-Dawley rats mechanically ventilated with gas containing 70% oxygen. Epinephrine and methoxamine but not saline placebo significantly increased coronary perfusion pressure from approximately 32 to 55 mm Hg. Following epinephrine, end-tidal PCO2 decreased from approximately 10 to 5 mm Hg. This was associated with a time-coincident decrease in PaO2 from approximately 130 to 74 mm Hg and an increase in PaCO2 from approximately 26 to 40 mm Hg. These changes indicated increases in alveolar dead space ventilation concomitant with increases in pulmonary arteriovenous admixture. No such effects were observed after administration of either methoxamine or saline placebo. Each of the 15 rats was successfully resuscitated. However, a significantly larger number of transthoracic countershocks were required after epinephrine compared with methoxamine or placebo before return of spontaneous circulation.

CONCLUSIONS

Epinephrine induced ventilation/perfusion during cardiopulmonary resuscitation as a result of redistribution of pulmonary blood flow.

Prostacyclin for the treatment of pulmonary hypertension in the adult respiratory distress syndrome: effects on pulmonary capillary pressure and ventilation-perfusion distributions

Nine patients who had developed pulmonary artery hypertension during the adult respiratory distress syndrome (ARDS) were treated with an infusion of prostacyclin (PGI2) (12.5-35.0 ng.kg-1.min-1). Whether PGI2 might decrease the pulmonary capillary pressure (PCP) obtained by analysis of the pulmonary artery occlusion pressure decay curve and improve systemic oxygen delivery was examined. Gas exchange alterations induced by PGI2 were analyzed by using the multiple inert gas elimination technique. PGI2 reduced the pulmonary artery pressure from 35.6 to 28.8 mmHg (P less than 0.001) and the PCP from 22.9 to 19.7 mmHg (P less than 0.01) without changing the contribution of the pulmonary venous resistance to the total pulmonary vascular resistance. The cardiac index increased from 4.2 to 5.7 1.min-1.m-2 (P less than 0.001) due to both increased stroke volume and heart rate. Despite a marked deterioration of ventilation-perfusion (VA/Q) matching with increased true intrapulmonary shunt flow from 28.6% to 38.6% (P less than 0.01) of the cardiac output, the PaO2 was unchanged due to increased mixed venous oxygen content indicated by an augmented mixed venous PO2 (from 37.0 to 41.9 mmHg, P less than 0.01). This caused a 35% (P less than 0.001) increase of the systemic oxygen delivery rate. Thus, short-term infusions of PGI2 reduced PAP and PCP without deleterious effects on arterial oxygenation in patients with ARDS. Hence, PGI2 may be useful to lower pulmonary vascular pressures in patients with ARDS.

Hypoxia-induced vasoconstriction in isolated perfused lungs exposed to injectable or inhalation anesthetics

Investigations during the last two decades have revealed a tendency to inpaired pulmonary gas exchange in patients during general anesthesia. In the awake state, arterial hypoxemia is counteracted by a mechanism which tends to normalize the ventilation/perfusion ratio of the lungs by way of a hypoxia-induced vasoconstriction in poorly ventilated areas. This results in a redistribution of perfusion to more adequately ventilated lung regions. Recent observations suggest, however, that this beneficial mechanism is blunted by some commonly used inhalation anesthetics. In the present study the effect of inhalation anesthetics and injectable anesthetics on the vasoconstrictor response to acute alveolar hypoxia have been compared in isolated blood-perfused rat lungs. The experiments showed that the response was unaffected by N2O and injectable anesthetics, while a reversible, dose-dependent damping effect was demonstrated for the volatile inhalation anesthetics, ether, halothane and methoxyflurance. The effect could be demonstrated at blood concentrations comparable to those used in clinical anesthesia, and it was not due to a general paralysis of the vascular smooth muscle. The findings might, at least in part, explain the occurrence of arterial hypoxemia during general inhalation anesthesia.

Prostaglandin E1 in the adult respiratory distress syndrome. Benefit for pulmonary hypertension and cost for pulmonary gas exchange

Prostaglandin E1 (PGE1) has been reported to improve survival in patients with the adult respiratory distress syndrome (ARDS). However, the effects of this pulmonary vasodilating compound on gas exchange have been little documented. We therefore measured hemodynamics, blood gases, and the distributions of ventilation-perfusion ratios (VA/Q), using the multiple inert gas elimination technique, at baseline and during infusion of PGE1 0.02 to 0.04 microgram.kg-1.min-1 in six patients with pulmonary hypertension secondary to ARDS ventilated with 10 cm H2O positive end-expiratory pressure. PGE1 decreased systemic arterial mean pressure (-16%) and pulmonary arterial mean pressure (-15%) and increased cardiac index (+20%) and heart rate (+11%). Arterial PO2 decreased from 99 +/- 6 to 77 +/- 8 mm Hg (p less than 0.01, mean +/- SEM) with no change in mixed venous PO2 and in O2 consumption. PGE1 increased true shunt from 21 +/- 4 to 32 +/- 5% of total blood flow (p less than 0.01) with no significant modification in the pattern of VA/Q distribution. Thus, in ARDS, pulmonary hypertension is reduced by PGE1 at the price of a deterioration in pulmonary gas exchange. The clinical relevance of these findings remains to be evaluated.

Improvement in ventilation-perfusion matching by almitrine in COPD

Almitrine, a peripheral chemoreceptor stimulating drug, was given 100 mg orally to six patients with advanced chronic obstructive pulmonary disease (COPD), and its effects on hemodynamics, blood gases, lung mechanics, and the distribution of ventilation/perfusion ratios (VA/Q), determined by the inert gas elimination technique, were investigated. Arterial Po2 increased from 52 +/- 4 to 59 +/- 3 mm Hg, mean +/- SEM, p less than 0.01, arterial Pco2 decreased from 46 +/- 3 to 43 +/- 3 mm Hg, p less than 0.05, and venous admixture from 30 +/- 6 to 19 +/- 3 percent, p less than 0.02. No change occurred in ventilation, variables of lung mechanics, systemic and pulmonary hemodynamics, except an increase in pulmonary vascular resistance (from 364 +/- 103 to 438 +/- 99 dyne.s.cm-5, p less than 0.05). A reduction in VA/Q inequality could be demonstrated with a redistribution of blood flow into the lungs by a diversion of 15 percent of total blood flow from units with low VA/Q (between 0.08 and 0.4) to units with normal VA/Q (between 0.5 and 1.8). These changes might be explained by an enhancement of hypoxic pulmonary vasoconstriction. Pharmacologic peripheral chemoreceptor stimulation, at an infra-ventilatory analeptic dosage, might be of therapeutic interest to patients with respiratory insufficiency due to VA/Q inequality.

Effects of vasodilators on hypoxic pulmonary vasoconstriction in normal man

A reduction of arterial PO2 is generally observed when vasodilators are given to patients with cardiac or pulmonary disease. This has been attributed to a release of preexisting hypoxic pulmonary vasoconstriction (HPV). We investigated the effects of hemodynamics and blood gases of IV nitroglycerin, IV nitroprusside and sublingual nifedipine, at dosages currently used in clinical practice, in 23 healthy volunteers at normoxic conditions (fraction of inspired O2, FIO2 0.21) and at acute inspiratory hypoxia (FIO2 0.125 during 10 min). Breathing FIO2 0.125 elicited pulmonary vasoconstriction in all the subjects. At FIO2 0.21, nitroglycerin reduced preload, nifedipine reduced afterload, nitroprusside had balanced effects, but none of the drugs induced pulmonary vasodilation and only nitroglycerin deteriorated arterial oxygenation. At FIO2 0.125, nitroglycerin did not at all affect the pulmonary pressor response, while both nitroprusside and nifedipine decreased it. An inhibition of HPV was obtained with certainty in only one subject who received nitroprusside. In all the subjects in whom HPV was partially inhibited by vasodilator administration, the alveolar-arterial PO2 gradients remained significantly lowered, suggesting that the pulmonary vascular tone adaptation to alveolar hypoxia still was effective in improving ventilation/perfusion relationships. The role of impaired HPV in the reduction of arterial PO2 in patients under vasodilator therapy may have to be reevaluated.

Ventilation-perfusion mismatching in acute severe asthma: effects of salbutamol and 100% oxygen

Ventilation-perfusion (VA/Q) relationships and gas exchange were studied by the multiple inert gas technique in 19 patients admitted to hospital with acute severe asthma (FEV1 41% predicted) before and during the administration of intravenous salbutamol, inhaled salbutamol, or 100% oxygen. Eight patients received a continuous intravenous infusion of salbutamol (4 micrograms/min, total dose 360 micrograms) and were studied before treatment, after 60 and 90 minutes of treatment, and one hour after treatment had been discontinued. Six patients had measurements before and 15 minutes after inhaling 300 micrograms salbutamol from a metered dose inhaler on two occasions (total dose 600 micrograms) and one hour after the last dose. Measurements were also made in five patients before and while they breathed 100% oxygen for 20 minutes. At baseline (fractional inspired oxygen (FiO2) 21%) all patients showed a broad unimodal (n = 10) or bimodal (n = 9) distribution of blood flow with respect to VA/Q. A mean of 10.5% of the blood flow was associated with low VA/Q units without any appreciable shunt. One of the best descriptors of VA/Q inequality, the second moment of the perfusion distribution on a log scale (log SD Q), was moderately high with a mean of 1.18 (SEM 0.08) (normal less than 0.6). Measures of VA/Q inequality correlated poorly with spirometric findings. After salbutamol the increase in airflow rates was similar regardless of the route of administration. Intravenous salbutamol, however, caused a significant increase in heart rate, cardiac output, and oxygen consumption (VO2); in addition, both perfusion to low VA/Q areas and log SD Q increased significantly. Inhaled salbutamol caused only minor changes in heart rate, cardiac output, VO2, and VA/Q inequality. Arterial oxygen tension (PaO2) remained unchanged during salbutamol administration, irrespective of the route of administration. During 100% oxygen breathing there was a significant increase in log SD Q (from 1.11 to 1.44). It is concluded that patients with acute severe asthma show considerable VA/Q inequality with a high level of pulmonary vascular reactivity. Despite similar bronchodilator effects from inhaled and intravenous salbutamol, VA/Q relationships worsened only during intravenous infusion. PaO2 remained unchanged, however, because the change in VA/Q relationships was associated with an increase in metabolic rate and cardiac output.

Effect of almitrine on ventilation-perfusion distribution in adult respiratory distress syndrome

Almitrine improves ventilation/perfusion relationships (VA/Q) in COPD, but its effects in ARDS, in which VA/Q mismatching is the cause of severe hypoxemia, are not known. The effects of almitrine on pulmonary gas exchange and circulation were assessed in 9 patients with ARDS who were sedated, paralyzed, and mechanically ventilated at constant FlO2 (range, 0.48 to 0.74). Systemic and pulmonary hemodynamics, conventional gas exchange, and the VA/Q distribution by the multiple inert gas elimination technique (MIGT) were measured before (baseline), during (ALM 15), at the end of (ALM 30), and at 30-min intervals after (POSTALM 30, 60, and 90) the intravenous infusion of 0.5 mg/kg body weight of almitrine over 30 min. Almitrine significantly increased PaO2 from 78 +/- 15 mm Hg to 140 +/- 49 at ALM 15 and 138 +/- 52 at ALM 30. AaPO2 and QS/QT decreased during the administration of the drug. The MIGT showed that almitrine redistributed pulmonary blood flow from shunt areas (reduction from 29 +/- 11 to 17 +/- 11% of QT) to lung units with normal VA/Q ratios (increase from 63 +/- 9 to 73 +/- 6% of QT). The Ppa increased from 26 +/- 5 to 30 +/- 5 mm Hg without changes in QT. Changes were transient, returning toward baseline 30 min after stopping the infusion of the drug. Almitrine significantly reduced the VA/Q inequalities present in ARDS and may be useful in the management of those patients.

Nitric oxide inhalation during exercise in chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) may develop hypoxemia and pulmonary hypertension when exercising. To investigate whether inhaled nitric oxide (NO), a selective pulmonary vasodilator, modifies the changes induced by exercise in pulmonary hemodynamics and gas exchange in COPD, we studied nine patients (FEV1, = 39 +/- 2% predicted), at rest and at submaximal exercise, during breathing of room air and NO (40 ppm). NO inhalation decreased pulmonary artery pressure (Ppa) both at rest and during exercise (analysis of variance [ANOVA] p < 0.05). However, the effect of NO on PaO2 was different at rest than during exercise. At rest, NO decreased PaO2 from 72 +/- 3 mm Hg to 65 +/- 2 mm Hg, due to an increase in ventilation-perfusion (VA/Q) inequality (dispersion of blood flow distribution from 0.9 +/- 0.1 to 1.1 +/- 0.1). During exercise, PaO2 decreased during breathing of room air (-5 +/- 3 mm Hg), whereas it remained essentially unchanged during inhalation of NO (+2 +/- 3 mm Hg), with both changes being significantly different (p < 0.05). VA/Q relationships improved during exercise during breathing of both room air and NO, as a result of a reduction in the dispersion of ventilation distribution. Moreover, NO administered on exertion contributed to redistribute blood flow from alveolar units with low VA/Q ratios to units with normal ratios (p < 0.05). We conclude that in patients with COPD, the inhalation of NO during exercise moderately reduces pulmonary hypertension, and that in contrast with the effects of such inhalation at rest, it may prevent the exercise-associated decrease of PaO2. This effect is probably explained by a preferential distribution of inhaled NO during exercise to well-ventilated alveolar units with faster time constants and normal VA/Q ratios.

Local effects of anesthetics on regional hypoxic pulmonary vasoconstriction

The hypothesis that halogenated anesthetics and N2O locally inhibit hypoxic pulmonary vasoconstriction (HPV) was tested. Selective ventilation of the left lower lobe of the lung with N2 in dogs anesthetized with pentobarbital caused blood flow to the lobe to decrease 55.5 +/- 2.0 per cent and lobar vascular resistance to increase 148 +/- 8 per cent. Responses to hypoxia were remeasured during administration of various MAC multiples of inhalation anesthetics to the left lower lobe and following systemic administration of intravenous anesthetics. Isoflurane and fluorexene progressively inhibited and finally almost extinguished the vasoconstriction response as anesthetic concentration increased to 3 MAC. N2O moderately diminished HPV. Halothane had little, and intravenous anesthetics had no, significant effect on HPV. It is concluded that N2O, isoflurane, and fluroxene locally inhibit regional HPV and via this mechanism may increase total venous admixture.

Influence of L-carnitine administration on maximal physical exercise

The effects of L-carnitine administration on maximal exercise capacity were studied in a double-blind, cross-over trial on ten moderately trained young men. A quantity of 2 g of L-carnitine or a placebo were administered orally in random order to these subjects 1 h before they began exercise on a cycle ergometer. Exercise intensity was increased by 50-W increments every 3 min until they became exhausted. After 72-h recovery, the same exercise regime was repeated but this time the subjects, who had previously received L-carnitine, were now given the placebo and vice versa. The results showed that at the maximal exercise intensity, treatment with L-carnitine significantly increased both maximal oxygen uptake, and power output. Moreover, at similar exercise intensities in the L-carnitine trial oxygen uptake, carbon dioxide production, pulmonary ventilation and plasma lactate were reduced. It is concluded that under these experimental conditions pretreatment with L-carnitine favoured aerobic processes resulting in a more efficient performance. Possible mechanisms producing this effect are discussed.

Response of premature infants with severe respiratory failure to inhaled nitric oxide. Preemie NO Collaborative Group

Elevated pulmonary vascular resistance is seen in premature infants with severe respiratory distress syndrome (RDS). Inhaled nitric oxide (NO) has been shown to decrease pulmonary vascular resistance and to improve oxygenation in some patients with respiratory failure. The purpose of this study was to determine whether premature infants with severe RDS would respond to inhaled NO with an improvement in oxygenation. Eleven premature infants (mean gestational age 29.8 weeks) with severe respiratory failure caused by RDS were treated with NO in four concentrations [1, 5, 10, 20 parts per million (ppm) NO] and with placebo (0 ppm NO). Arterial blood gas measurements were drawn immediately before and at the end of each of the 15-minute treatments and were used to determine the arterial/alveolar oxygen ratio (PaO2/PAO2). Ten of the 11 infants had a greater than 25% increase in PaO2/PAO2. Five of the 11 had a greater than 50% increase in PaO2/PAO2. Despite normal cranial ultrasound imaging prior to NO, 3 infants had intracranial hemorrhage (ICH) noted on their first ultrasound scan after this brief period of NO treatment, and 4 additional infants developed ICH later during their hospitalization. No infant had significant elevations of methemoglobin concentrations after the total 60-minute exposure to NO. NO may be an effective method of improving oxygenation in infants with severe RDS. The disturbing incidence of ICH in this small group of infants needs to be carefully evaluated before considering routine use or NO for preterm infants.

Effects of oral narcotics on sleep-disordered breathing in healthy adults

Alcohol and benzodiazepines may increase sleep-disordered breathing by decreasing activity of pharyngeal dilating muscles, favoring the development of obstructive apneas and hypopneas. Narcotics cause greater depression of wakeful respiration than the previously mentioned drugs; however, the influence of narcotics on the upper airway and breathing during sleep has not been studied. We, therefore, examined, in 12 healthy adults, the effects of oral hydromorphone hydrochloride (2 and 4 mg) on breathing during sleep and on a variety of awake respiratory variables (minute ventilation, gas exchange, and chemoresponsiveness). In addition, awake pharyngeal inspiratory airflow resistance was determined before and after narcotic administration to assess the drug's influence on patency of the upper airway. Following both doses, minute ventilation decreased, and carbon dioxide pressure increased. The 4-mg dose of hydromorphone hydrochloride also produced a significant decrement in the hypoxic ventilatory response, whereas hypercapnic responsiveness and pharyngeal resistance did not change following either dose of the drug. Despite the respiratory depression during wakefulness described previously, no significant change was observed in any measure of sleep-disordered breathing after either dose of narcotic. We conclude that in healthy individuals without suspected sleep apnea, oral hydromorphone in standard dosages does not significantly increase sleep-disordered breathing. This result may be due to a lack of selective depression of upper-airway muscular function by the doses of narcotic used.

Oxygen transport and cardiovascular responses in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) exposed to acute hypoxia

Responses to acute hypoxia were measured in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) (approximately 1-3 kg body weight). Fish were prevented from making swimming movements by a spinal injection of lidocaine and were placed in front of a seawater delivery pipe to provide ram ventilation of the gills. Fish could set their own ventilation volumes by adjusting mouth gape. Heart rate, dorsal and ventral aortic blood pressures, and cardiac output were continuously monitored during normoxia (inhalant water (PO2 greater than 150 mmHg) and three levels of hypoxia (inhalant water PO2 approximately 130, 90, and 50 mmHg). Water and blood samples were taken for oxygen measurements in fluids afferent and efferent to the gills. From these data, various measures of the effectiveness of oxygen transfer, and branchial and systemic vascular resistance were calculated. Despite high ventilation volumes (4-7 l.min-1.kg-1), tunas extract approximately 50% of the oxygen from the inhalant water, in part because high cardiac outputs (115-132 ml.min-1.kg-1) result in ventilation/perfusion conductance ratios (0.75-1.1) close to the theoretically ideal value of 1.0. Therefore, tunas have oxygen transfer factors (ml O2.min-1.mmHg-1.kg-1) that are 10-50 times greater than those of other fishes. The efficiency of oxygen transfer from water in tunas (approximately 65%) matches that measured in teleosts with ventilation volumes an order of magnitude lower. The high oxygen transfer factors of tunas are made possible, in part, by a large gill surface area; however, this appears to carry a considerable osmoregulatory cost as the metabolic rate of gills may account for up 70% of the total metabolism in spinally blocked (i.e., non-swimming) fish. During hypoxia, skipjack and yellowfin tunas show a decrease in heart rate and increase in ventilation volume, as do other teleosts. However, in tunas hypoxic bradycardia is not accompanied by equivalent increases in stroke volume, and cardiac output falls as HR decreases. In both tuna species, oxygen consumption eventually must be maintained by drawing on substantial venous oxygen reserves. This occurs at a higher inhalant water PO2 (between 130 and 90 mmHg) in skipjack tuna than in yellowfin tuna (between 90 and 50 mmHg). The need to draw on venous oxygen reserves would make it difficult to meet the oxygen demand of increasing swimming speed, which is a common response to hypoxia in both species.(ABSTRACT TRUNCATED AT 400 WORDS)

Arterial oxygenation and arterial oxygen transport in chronic myocardial failure at rest, during exercise and after hydralazine treatment

Arterial oxygen transport (cardiac output x arterial oxygen content) may be decreased in heart failure. We studied the determinants of arterial oxygen transport in 15 patients with chronic, severe myocardial failure at rest and during cycle ergometry. During control therapy at rest, arterial oxygen tension was normal (81 +/- 8 mm Hg, mean +/- SD) and increased slightly during exercise (90 +/- 14 mm Hg). During hydralazine therapy at rest, arterial oxygen tension was slightly higher (87 +/- 9 mm Hg) and also increased during exercise (92 +/- 15 mm Hg). Hydralazine did not increase arterial oxygen tension (0.10 greater than p greater than 0.05), but exercise did (p less than 0.02). Arterial oxygen saturation and content were normal and did not change under any condition or treatment. During control therapy at rest, arterial oxygen transport was low (313 +/- 74 ml/min . m2) and remained abnormally low during exercise (434 +/- 124 ml/min . m2). During hydralazine therapy, arterial oxygen transport was higher at rest (457 +/- 100 ml/min . m2) and during exercise (577 +/- 131 ml/min . m2). Hydralazine increased arterial oxygen transport (p less than 0.01) because it increased stroke volume at rest and during exercise, but it did not change arterial oxygenation. Arterial oxygenation is normal in chronic heart failure patients at rest and during exercise. Hydralazine increases cardiac output and arterial oxygen transport without changing arterial oxygenation.

Positive end-expiratory pressure improves gas exchange and pulmonary mechanics during partial liquid ventilation

Partial liquid ventilation (PLV) with perflubron (PFB) has been proposed as an adjunct to the current therapies for the acute respiratory distress syndrome (ARDS). Because PFB has been also referred to as "liquid PEEP," distributing to the most gravity-dependent regions of the lung, less attention has been paid to the amount of applied positive end-expiratory pressure (PEEP). We hypothesized that higher PEEP levels than currently applied are needed to optimize gas exchange, and that the lower inflection point (LIP) of the pressure-volume curve could be used to estimate the amount of PEEP needed when the lung is filled with PFB. Lung injury was induced in 23 sheep by repeated lung lavage with warmed saline until the PaO2/FIO2 ratio fell below 150. Five sheep were used to investigate the change of the LIP when the lung was filled with PFB in increments of 5 ml/kg/body weight to a total of 30 ml/kg/body weight. To evaluate the impact of PEEP set at LIP +1 cm H2O we randomized an additional 15 sheep to three groups with different doses (7.5 ml, 15 ml, 30 ml/kg/body weight) of PFB. In random order a PEEP of 5 cm H2O or PEEP at LIP +1 cm H2O was applied. The LIP decreased with incremental filling of PFB to a minimum at 10 ml (p < 0.05). Increasing PEEP from below LIP to LIP +1 cm H2O at 15 and 30 ml/kg resulted in an improvement in PaO2 from 152 +/- 36 to 203 +/- 68 (NS) and 193 +/- 57 to 298 +/- 80 (p < 0.05), respectively. Pulmonary shunt, and ratio of dead space volume to tidal volume (VD/VT) decreased, and static lung compliance increased with PEEP at LIP +1 cm H2O (p < 0.05). No changes were observed in hemodynamics. We conclude that increasing the dose of PFB shifts the LIP to the left, and that setting PEEP at LIP +1 cm H2O improves gas exchange at moderate to high doses of PFB.

Depression of hypoxic ventilatory response by nitrous oxide

Ventilatory responses to CO2 and hypoxia were measured in four normal volunteers breathing 30-50 per cent N2O with and without added inspiratory resistance. CO2 response was measured by a steady-state technique, hypoxic response by a non-steady-state progressive technique. Added inspiratory resistance depressed ventilatory responses to both CO2 and hypoxia. N2O had no effect on CO2 response either with or without resistance. N2O depressed the ventilatory response to hypoxia without added resistance and further depressed the response measured with added resistance. It is thought that this was probably the result of selective depression of peripheral chemoceptor function by N2O.