Hypoxemia following the administration of sublingual nitroglycerin

Reducing Pulmonary Capillary Wedge Pressure During Exercise Exacerbates Exertional Dyspnea in Patients With Heart Failure With Preserved Ejection Fraction: Implications for V˙/Q˙ Mismatch

BACKGROUND

The primary cause of dyspnea on exertion in heart failure with preserved ejection fraction (HFpEF) is presumed to be the marked rise in pulmonary capillary wedge pressure during exercise; however, this hypothesis has never been tested directly. Therefore, we evaluated invasive exercise hemodynamics and dyspnea on exertion in patients with HFpEF before and after acute nitroglycerin (NTG) treatment to lower pulmonary capillary wedge pressure.

RESEARCH QUESTION

Does reducing pulmonary capillary wedge pressure during exercise with NTG improve dyspnea on exertion in HFpEF?

STUDY DESIGN AND METHODS

Thirty patients with HFpEF performed two invasive 6-min constant-load cycling tests (20 W): one with placebo (PLC) and one with NTG. Ratings of perceived breathlessness (0-10 scale), pulmonary capillary wedge pressure (right side of heart catheter), and arterial blood gases (radial artery catheter) were measured. Measurements of V˙/Q˙ matching, including alveolar dead space (Vdalv; Enghoff modification of the Bohr equation) and the alveolar-arterial Po2 difference (A-aDO2; alveolar gas equation), were also derived. The ventilation (V˙e)/CO2 elimination (V˙co2) slope was also calculated as the slope of the V˙e and V˙co2 relationship, which reflects ventilatory efficiency.

RESULTS

Ratings of perceived breathlessness increased (PLC: 3.43 ± 1.94 vs NTG: 4.03 ± 2.18; P = .009) despite a clear decrease in pulmonary capillary wedge pressure at 20 W (PLC: 19.7 ± 8.2 vs NTG: 15.9 ± 7.4 mm Hg; P < .001). Moreover, Vdalv (PLC: 0.28 ± 0.07 vs NTG: 0.31 ± 0.08 L/breath; P = .01), A-aDO2 (PLC: 19.6 ± 6.7 vs NTG: 21.1 ± 6.7; P = .04), and V˙e/V˙co2 slope (PLC: 37.6 ± 5.7 vs NTG: 40.2 ± 6.5; P < .001) all increased at 20 W after a decrease in pulmonary capillary wedge pressure.

INTERPRETATION

These findings have important clinical implications and indicate that lowering pulmonary capillary wedge pressure does not decrease dyspnea on exertion in patients with HFpEF; rather, lowering pulmonary capillary wedge pressure exacerbates dyspnea on exertion, increases V˙/Q˙ mismatch, and worsens ventilatory efficiency during exercise in these patients. This study provides compelling evidence that high pulmonary capillary wedge pressure is likely a secondary phenomenon rather than a primary cause of dyspnea on exertion in patients with HFpEF, and a new therapeutic paradigm is needed to improve symptoms of dyspnea on exertion in these patients.

Analytic Reviews : Hypoxic Pulmonary Vasoconstriction: Physiology and Pathophysiology

Hypoxic pulmonary vasoconstriction is the unique re sponse of the lung circulation to ventilation with hy poxic gas, resulting in an increase in pulmonary arterial pressure and vascular resistance. The site of hypoxic vasoconstriction is the small pulmonary arteries. The hypoxic pressor response optimizes ventilation and per fusion matching and thus preserves arterial oxygen ten sion. The mechanism of this response is not clear, al though considerable knowledge has been gained about its modulation. We review the current state of under standing of the physiology and pathophysiology of hy poxic pulmonary vasoconstriction.

Hypoxic pulmonary vasoconstriction: physiology and anesthetic implications

Hypoxic pulmonary vasoconstriction (HPV) represents a fundamental difference between the pulmonary and systemic circulations. HPV is active in utero, reducing pulmonary blood flow, and in adults helps to match regional ventilation and perfusion although it has little effect in healthy lungs. Many factors affect HPV including pH or PCO2, cardiac output, and several drugs, including antihypertensives. In patients with lung pathology and any patient having one-lung ventilation, HPV contributes to maintaining oxygenation, so anesthesiologists should be aware of the effects of anesthesia on this protective reflex. Intravenous anesthetic drugs have little effect on HPV, but it is attenuated by inhaled anesthetics, although less so with newer agents. The reflex is biphasic, and once the second phase becomes active after about an hour of hypoxia, this pulmonary vasoconstriction takes hours to reverse when normoxia returns. This has significant clinical implications for repeated periods of one-lung ventilation.

The role of ion channels in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an important mechanism by which localized flow of blood in small resistance pulmonary arteries is matched to alveolar ventilation. This chapter discusses the role of several potassium and calcium channels in HPV, both in enhancing calcium influx into smooth muscle cells (SMCs) and in stimulating the release of calcium from the sarcoplasmic reticulum, thus increasing cytosolic calcium. The increase in calcium sensitivity caused by hypoxia is reviewed in Chapter 19. Particular attention is paid to the activity of the L-type calcium channels which increase calcium influx as a result of membrane depolarization and also increase calcium influx at any given membrane potential in response to hypoxia. In addition, activation of the L-type calcium channel may, in the absence of any calcium influx, cause calcium release from the sarcoplasmic reticulum. Many of these mechanisms have been reported to be involved in both HPV and in normoxic contraction of the ductus arteriosus.

Mechanisms of oxygen sensing: a key to therapy of pulmonary hypertension and patent ductus arteriosus

Specialized tissues that sense acute changes in the local oxygen tension include type 1 cells of the carotid body, neuroepithelial bodies in the lungs, and smooth muscle cells of the resistance pulmonary arteries and the ductus arteriosus (DA). Hypoxia inhibits outward potassium current in carotid body type 1 cells, leading to depolarization and calcium entry through L-type calcium channels. Increased intracellular calcium concentration ([Ca+ +]i) leads to exocytosis of neurotransmitters, thus stimulating the carotid sinus nerve and respiration. The same K+ channel inhibition occurs with hypoxia in pulmonary artery smooth muscle cells (PASMCs), causing contraction and providing part of the mechanism of hypoxic pulmonary vasoconstriction (HPV). In the SMCs of the DA, the mechanism works in reverse. It is the shift from hypoxia to normoxia that inhibits K+ channels and causes normoxic ductal contraction. In both PA and DA, the contraction is augmented by release of Ca+ + from the sarcoplasmic reticulum, entry of Ca+ + through store-operated channels (SOC) and by Ca+ + sensitization. The same three 'executive' mechanisms are partly responsible for idiopathic pulmonary arterial hypertension (IPAH). While vasoconstrictor mediators constrict both PA and DA and vasodilators dilate both vessels, only redox changes mimic oxygen by having directly opposite effects on the K+ channels, membrane potential, [Ca(++)]i and tone in the PA and DA. There are several different hypotheses as to how redox might alter tone, which remain to be resolved. However, understanding the mechanism will facilitate drug development for pulmonary hypertension and patent DA.

Human pulmonary vascular responses to hypoxia and hypercapnia

The ability of alveolar gas composition to influence pulmonary vascular tone has been appreciated for over 50 years. In particular, it has been proposed that both O2 and CO2 could play a role in the matching of perfusion to ventilation within the lung, improving the overall efficiency of gas exchange. A wide variety of experimental approaches has been used to investigate pulmonary vascular effects of the respiratory gases in a range of mammalian species. In this article, we review experiments performed in healthy humans, identify particular difficulties in the interpretation of such experiments, and discuss possible approaches to future study.

Adult isolated hypoplasia of left pulmonary artery with exertional angina and abnormal exercise stress test: a case report and treatment implication

Pulmonary artery hypoplasia, either congenital or acquired, is a rare abnormality seen in adults. We reported the first case of adult, isolated, left pulmonary artery hypoplasia, with exertional angina and prominent ST depression in exercise stress test, that seemed to be caused by exertional hypoxemia. Several vasodilators, including nitroglycerin, prostaglandin E1, and nifedipine, were administered individually, each with subsequent hemodynamic monitoring, pulse oximetric monitoring, and exercise test. Vasodilator administrations reduced pulmonary vascular resistance (baseline, 599; vasodilators, 306, 211, and 284 dyne x sec x m2/cm5, respectively) and attenuated ST depression (by 52, 72, and 27%, respectively) but without an immediate benefit on exercise tolerance. All vasodilators except nifedipine ameliorated exertional hypoxemia (expressed by arterial oxygen saturation during peak exercise, baseline, 69%; vasodilators, 85, 78, and 65%, respectively). Additional oxygen supply after nitroglycerin administration further benefited exertional hypoxemia (arterial oxygen saturation, 96%) and exercise ST depression (attenuated by 82%).

Atrial natriuretic peptide and brain natriuretic peptide in cor pulmonale. Hemodynamic and endocrine effects

We have studied the hemodynamic and hormonal effects of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in eight patients with cor pulmonale. Subjects were studied twice and were given a 20-min placebo infusion followed by either ANP or BNP (3 pmol/kg/min then 10 pmol/kg/ min for 20 min each). Responses were measured after placebo infusion and following low-dose then high-dose ANP or BNP. Placebo infusion had no significant effects on either study day. Low-dose ANP and BNP significantly reduced mean pulmonary artery pressure (MPAP) from baseline by 3.7 mm Hg (95% confidence interval [CI], 1.4 to 6.1) and 3.0 mm Hg (95% CI, 0.6 to 5.4), respectively. High-dose ANP and BNP further reduced MPAP from baseline by 7.1 mm Hg (95% CI, 4.8 to 9.4) and 7.1 mm Hg (95% CI, 4.7 to 9.6), respectively. Effects on total pulmonary vascular resistance were similar. ANP and BNP had no confounding systemic hemodynamic effects. Plasma aldosterone was significantly suppressed from baseline by ANP: 156 pmol/L (95% CI, 93 to 220) after low dose, 275 pmol/L (95% CI, 207 to 343) after high dose; and by BNP: 92 pmol/L (95% CI, 30 to 153) after low dose, 159 pmol/L (95% CI, 98 to 220) after high dose. ANP and BNP produced dose-related pulmonary vasodilatation in patients with cor pulmonale, without worsening oxygen saturation or affecting systemic hemodynamics. ANP and BNP also exerted favorable neurohormonal effects by suppressing aldosterone.

Lisinopril attenuates acute hypoxic pulmonary vasoconstriction in humans

OBJECTIVE

We have studied the effects of angiotensin-converting enzyme (ACE) inhibition with lisinopril on acute hypoxic pulmonary vasoconstriction (HPV).

DESIGN

Randomized, double-blind, placebo-controlled study in ten healthy volunteers. Subjects received four daily doses of lisinopril or matched placebo before attending the laboratory 5 h after taking the final dose. After reaching a resting hemodynamic state, subjects were made hypoxemic (SaO2, 75 to 80%) for 30 min.

MEASUREMENTS

Pulmonary and systemic hemodynamic parameters were measured noninvasively at baseline and after 30 min of hypoxemia.

RESULTS

Mean pulmonary artery pressure (MPAP) and total pulmonary vascular resistance (TPR) were similar at baseline on both study days. The increase in MPAP induced by hypoxemia was significantly blunted by pretreatment with lisinopril (means and 95% confidence interval [CI] for difference) 13.4 mm Hg vs placebo 19.6 mm Hg (95% CI, 2.5, 9.9). Likewise, the TPR response to hypoxemia was significantly blunted by lisinopril: 124 dyne.s.cm-5 vs placebo 179 dyne.s.cm-5 (95% CI, 11, 99). Lisinopril had no confounding systemic effects on mean arterial pressure, cardiac output, or systemic vascular resistance at baseline or in response to hypoxemia.

CONCLUSIONS

Lisinopril therefore significantly attenuated the pulmonary pressor response to hypoxemia without decreasing baseline MPAP or TPR. This suggests that angiotensin II might play a modulatory role during HPV in man and that ACE inhibition may be a useful adjunctive treatment in hypoxemic pulmonary hypertension.

Hypoxic contraction of cultured pulmonary vascular smooth muscle cells

The cellular events involved in generating the hypoxic pulmonary vasoconstriction response are not clearly understood, in part because of the multitude of factors that alter pulmonary vascular tone. The goal of the present studies was to determine if a cell culture preparation containing vascular smooth muscle (VSM) cells could be made to contract when exposed to a hypoxic atmosphere. Cultures containing only fetal bovine pulmonary artery VSM cells were assessed for contractile responses to hypoxic stimuli by two methods. In the first, tension forces generated by cells grown on a flexible growth surface (polymerized polydimethyl siloxane) were manifested as wrinkles and distortions of the surface under the cells. Wrinkling of the surface was noted to progressively increase with time as the culture medium bathing the cells was made hypoxic (PO2 approximately 25 mmHg). The changes were sometimes reversible upon return to normoxic conditions and appeared to be enhanced in cells already exhibiting evidence of some baseline tone. Repeated passage in culture did not diminish the hypoxic response. Evidence for contractile responses to hypoxia was also obtained from measurements of myosin light chain (MLC) phosphorylation. Conversion of MLC to the phosphorylated species is an early step in the activation of smooth muscle contraction. Lowering the PO2 in the culture medium to 59 mmHg caused a 45% increase in the proportion of MLC in the phosphorylated form as determined by two-dimensional gel electrophoresis. Similarly, cultures preincubated for 4 h with 32P and then exposed to normoxia or hypoxia for a 5-min experimental period showed more than twice as much of the label in MLCs of the hypoxic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Stability of arterial to end-tidal carbon dioxide gradients during postoperative cardiorespiratory support

The changes in the arterial to end-tidal carbon dioxide gradient. P(a-ET)CO2, were studied in postoperative cardiac surgery patients from the time of admission to the intensive care unit, during changing cardiorespiratory support, up to the time of tracheal extubation. Individual factors evaluated for their effects on P(a-ET)CO2 included rate of mechanical ventilation, infusion of vasoactive agents (nitroglycerin, nitroprusside, dopamine, dobutamine, and metariminol), and associated changes in haemodynamic pathophysiology (cardiac index, pulmonary artery pressure, pulmonary vascular resistance index, systemic vascular resistance index, and pulmonary capillary wedge pressure). After approval by the Clinical Investigation Committee, 59 patients, age 63 +/- 9 (41 to 75) yr, were studied and 382 individual gradient determinations made. Mean P(a-ET)CO2 was 5.47 +/- 5.21 mmHg, with the mean PaCO2, 36.51 +/- 5.89 mmHg and mean ETCO2, 31.04 +/- 6.44 mmHg. For the population as a whole, the correlation between PaCO2 and ETCO2 determined by regression analysis was maintained (R = 0.644, P less than 0.001). Comparison of the individual and population correlation coefficients by Student's t test showed no significant difference, but a normal population distribution of the gradients (P less than 0.05). None of the variables assessed could be determined to influence P(a-ET)CO2 significantly. For many of the individual patients, however, the relationship between PaCO2 and ETCO2 did not maintain a significant correlation throughout the study period. In the postoperative cardiac surgery patient population P(a-ET)CO2 follows a normal distribution and PaCO2 and ETCO2 maintain a statistically significant correlation. However, when evaluating individual patients, this relationship has wide variability.

Pulmonary gas exchange effects by nitroglycerin, dopamine and dobutamine during one-lung ventilation in man

The effects of nitroglycerin, dopamine and dobutamine on pulmonary gas exchange were determined in 21 adult patients during two-lung and one-lung ventilation. Nitroglycerin, in 1 microgram.kg-1.min-1, decreased cardiac index (CI) and PaO2 during both two- and one-lung ventilation, and increased in Qs/Qt during one-lung ventilation. There were no significant changes in the measured variables during infusion of dopamine, 5 microgram.kg-1.min-1. Dobutamine, 5 microgram.kg-1.min-1, increased CI and PaO2 did not change during two-lung ventilation. During one-lung ventilation, PaO2 increased from (mean value +/- SD) 168 +/- 46 to 201 +/- 52 mmHg (P less than 0.01) with dobutamine infusion. Qs/Qt decreased from 29.2 +/- 7.0 to 26.0 +/- 6.2 per cent (P less than 0.05) without any change in pulmonary vascular resistance index during one-lung ventilation. We conclude that dobutamine has advantages over dopamine and nitroglycerin during one-lung ventilation.

Systemic and regional hemodynamic effects of isosorbide dinitrate in patients with liver cirrhosis and portal hypertension

In a group of 17 cirrhotic patients with portal hypertension, we have investigated the effects of 5 mg sublingual administration of isosorbide dinitrate (IDN) on central hemodynamics, on regional (hepatic and renal) hemodynamics and on blood gases. Fifteen min after drug administration, we observed a decrease in the right atrial mean pressure from 4 +/- 1 to 3 +/- 1 mmHg (mean +/- S.E.M., P less than 0.02) and of pulmonary arterial wedge pressure from 7 +/- 1 to 4 +/- 1 mmHg (P less than 0.001) with decreases of the cardiac index from 4.2 +/- 0.2 to 3.7 +/- 0.2 l/min/m2 (P less than 0.001) and the mean arterial pressure from 89 +/- 4 to 72 +/- 3 mmHg (P less than 0.001) and an increase in heart rate from 86 +/- 4 to 94 +/- 5 beats/min (P less than 0.001). Arterial PO2 decreased from 73 +/- 2 to 66 +/- 2 mmHg (P less than 0.001). As a consequence of both cardiac index and arterial PO2 reductions, O2 transport to the tissues was reduced from 602 +/- 32 to 518 +/- 26 ml/min.m2 (P less than 0.001). The hepatic venous pressure gradient decreased from 17 +/- 1 to 14 +/- 1 mmHg (P less than 0.001) and hepatic vein PO2 did not change. The hepatic blood flow (HBF) determined in 7 patients remained unchanged. Renal blood flow (RBF) determined in 5 patients decreased from 0.76 +/- 0.11 to 0.68 +/- 0.11 l/min (P less than 0.001). In conclusion, isosorbide dinitrate reduces portal hypertension in patients with liver cirrhosis without compromising hepatic perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nifedipine on arterial oxygenation at rest and during exercise in patients with stable angina

The effects of nifedipine on arterial oxygenation and hemodynamics were studied at rest and during bicycle exercise in 12 men (mean age 55 years, range 41 to 67) with stable exertional angina. The study was conducted double-blind on 2 days, 1 week apart, using a placebo-controlled crossover design. On each day, measurements at rest were made before and 20 minutes after 20 mg sublingual nifedipine or placebo and were followed by measurements made during exercise. Compared with placebo, nifedipine reduced mean arterial pressure, systemic vascular resistance and pulmonary vascular resistance, and increased heart rate and cardiac output at rest and during exercise. It did not alter mean pulmonary artery or pulmonary artery wedge pressures at rest, but decreased them during exercise. Nifedipine decreased arterial oxygen tension (PaO2) from 96 +/- 10 to 90 +/- 13 mm Hg (p less than 0.05) at rest and from 99 +/- 11 to 92 +/- 12 mm Hg (p less than 0.005) at submaximal exercise (33 +/- 21 W), but did not alter it (100 +/- 12 versus 100 +/- 16 mm Hg, p = NS) at maximal exercise (68 +/- 30 W). The reduction in PaO2 was not due to alveolar hypoventilation, because nifedipine did not alter arterial carbon dioxide tension, or to changes in mixed venous oxygen tension, which nifedipine increased at rest (39 +/- 2 versus 43 +/- 3 mm Hg, p less than 0.001) and during submaximal exercise (31 +/- 4 versus 33 +/- 4 mm Hg, p less than 0.03) and maximal exercise (27 +/- 3 versus 31 +/- 3 mm Hg, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of intranasally administered nitroglycerin on the blood pressure response to laryngoscopy and intubation in patients undergoing coronary artery by-pass surgery

The effect of intranasally administered nitroglycerin (NTG) on the cardiovascular response to laryngoscopy and intubation was studied. Thirty patients scheduled to undergo coronary artery by-pass surgery under thiopentone, enflurane and pancuronium anaesthesia were randomly divided into three groups. Group I received lignocaine 1.5 mg/kg i.v. prior to laryngoscopy and intubation (control group). Group II received lignocaine 1.5 mg/kg i.v. and in addition 2 mg nitroglycerin (NTG) was given intranasally. Group III received only 2 mg NTG intranasally. In Group I laryngoscopy and intubation caused a significant increase in mean arterial pressure (MAP) (P less than 0.01), heart rate (HR) (P less than 0.01) and rate pressure product (RPP) (P less than 0.01) compared to preoxygenation values. In Group II and III MAP and RPP remained unchanged, whereas HR increased (P less than 0.01 and P less than 0.01 respectively). It can be concluded that intranasally administered NTG effectively attenuates the pressor response to laryngoscopy and intubation in patients presenting for coronary artery by-pass surgery and that it is more effective and convenient method than intravenous lignocaine.

The site and mechanism of oxygen sensing for the pulmonary vessels

Lung vessels are unique in the body in that they react to hypoxia with constriction rather than dilatation. Whether this characteristic is inherent in the lung vessel or is due to an influence from a sensor in the surrounding lung parenchyma is not resolved. Recent data, however, showing that vascular hypoxia as well as airway hypoxia can produce pulmonary vasoconstriction and that the sensor for alveolar hypoxia is upstream in the precapillary vessels, allows but does not prove the precapillary pulmonary artery itself to be the O2 sensor. In addition, with the elimination of the mast cell as a necessary extravascular sensor for hypoxia at least in the mouse, there is no good candidate for an extravascular sensor for hypoxic pulmonary vasoconstriction.

Cardiorespiratory effects of isosorbide dinitrate and nifedipine in combination with nadolol: a double-blind comparative study of beneficial and adverse antianginal drug interactions

Combinations of 2 or 3 drugs are often used to treat angina pectoris, but their combined cardiorespiratory effects have not been investigated. Using a randomized, double-blind, placebo-controlled protocol, the effects of nadolol alone and nadolol in combination with isosorbide dinitrate and nifedipine were compared, in low and high doses, on antianginal efficacy, respiratory functions and arterial blood oxygen saturation (SaO2) in 19 patients with stable angina pectoris. A complete assessment including a bicycle exercise test with the measurement of the sum of ST-segment depression in all leads (sigma ST) was carried out every 2 weeks. The frequency of anginal attacks and nitroglycerin consumption was reduced significantly (p less than 0.001) by nadolol alone and in combination with the other drugs. Nadolol caused a slight reduction in the forced expiratory volume in 1 second, which was improved by isosorbide dinitrate and nifedipine. The sigma ST profile (basal, at peak exercise and 2 and 5 minutes after exercise) was decreased by nadolol alone and in combination with the other drugs, although the greatest reduction was achieved with large doses of nifedipine and nadolol. The rest and postexercise SaO2 decreased after nadolol alone and in combination with isosorbide dinitrate, but recovered to pretrial values after nifedipine and nadolol. With all drug combination, sigma ST depression was greater when the postexercise SaO2 was less than 92%, and decreased (p less than 0.05) in the same patients when their postexercise SaO2 was greater than 92%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nitroglycerin on central haemodynamics and VA/Q distribution during ventilation with FIO2 = 1.0 in patients after coronary bypass surgery

The effects of nitroglycerin (TNG) infusion during ventilation with FIO2 = 1.0 on central haemodynamics and the distribution of ventilation-perfusion (VA/Q) were studied with the multiple inert gas elimination technique in eight patients after coronary bypass surgery. Administration of TNG resulted in a significant decrease in mean arterial pressure, and an increase in heart rate while cardiac output remained unchanged. Mean right atrial, pulmonary arterial and pulmonary wedge pressures all decreased. There was a significant reduction in PaO2 from 50.5 to 32.7 kPa, while Pao2 remained unchanged in a control group of eight patients. This was mainly due to an increase in shunt from 9.3 to 16.5% of cardiac output during TNG-infusion. In the control group there was also an increase in shunt from 9.7 to 12.1% of cardiac output with a simultaneous decrease of the same magnitude in perfusion of regions with low VA/Q (0.005-0.1). This was not evident in the group receiving TNG. Twenty min after termination of TNG-infusion the effects on central haemodynamics and gas exchange were not fully reversed. The mechanism behind the increase in inert gas shunt observed with infusion of TNG during oxygen breathing is probably a selective effect on vessels with remaining high vasomotor tone despite high alveolar oxygen tension.

The acute effects of low flow oxygen and isosorbide dinitrate on left and right ventricular ejection fractions in chronic obstructive pulmonary disease

The objectives of this study were to determine the effects of low flow oxygen and isosorbide dinitrate on rest and exercise biventricular ejection fractions in patients with chronic obstructive pulmonary disease and to relate these ejection fraction responses to changes in pressure and flow. Nine patients with stable, moderate to severe chronic obstructive pulmonary disease who had no prior history of heart failure performed supine exercise with simultaneous hemodynamic and radionuclide ventriculographic monitoring. Eight patients performed a second exercise during low flow oxygen breathing and five performed a third exercise after ingesting 10 mg oral isosorbide. Oxygen led to a decrease in exercise pulmonary artery pressure in all subjects and a decline in total pulmonary resistance in five of the seven in whom it was measured. Right ventricular ejection fraction increased 0.05 or more only in subjects who had a decrease in total pulmonary resistance. Isosorbide fed to an increase in rest and exercise right and left ventricular ejection fractions with simultaneous decreases in pulmonary artery pressure, total pulmonary resistance, blood pressure and arterial oxygen tension. These results suggest that in patients with chronic obstructive pulmonary disease but without a history of right heart failure, the right ventricular systolic functional response to low flow oxygen and isosorbide at rest and exercise is, in part, determined by changes in total pulmonary resistance. The chronic relation between right ventricular ejection fraction and pulmonary hemodynamics in patients with chronic obstructive pulmonary disease remains to be evaluated.

Beneficial effects of dopamine combined with intravenous nitroglycerin on hemodynamics in patients with severe left ventricular failure

Hemodynamic effects of dopamine and intravenous nitroglycerin alone, and in combination, were studied in 27 patients with severe left ventricular failure. Dopamine alone increased cardiac index from 1.8 to 2.5 l/min/m2 but also increased wedge pressure from 24 to 30 mm Hg and heart rate from 88 to 101 beats/min. Arterial oxygen saturation fell from 92% to 87% (p less than .001). Nitroglycerin alone had a lesser effect on cardiac index (1.8 to 2.2 l/min/m2) but decreased wedge pressure from 26 to 16 mm Hg and heart rate from 91 to 86 beats/min. Arterial oxygen saturation fell from 91% to 90% (NS). Combined dopamine and nitroglycerin administration resulted in optimal hemodynamics, with cardiac index of 2.9 l/min/m2, wedge pressure of 17 mm Hg, and heart rate of 96 beats/min. Arterial oxygen saturation remained low at 88% in spite of the reduction in left ventricular filling pressure, which probably reflects increased intrapulmonary right-to-left shunting coupled with increased pulmonary blood flow. These results suggest that the combination of dopamine with intravenous nitroglycerin should be considered for patients with severe left ventricular dysfunction who require temporary pharmacologic support.

Contrasting acute effects of vasodilators (nitroglycerin, nitroprusside, and hydralazine) on right ventricular performance in patients with chronic obstructive pulmonary disease and pulmonary hypertension: a combined radionuclide-hemodynamic study

Fourteen patients with chronic obstructive pulmonary disease, mild to moderate pulmonary hypertension, and diminished right ventricular (RV) ejection fraction were studied acutely with use of a combined radionuclide-hemodynamic approach to assess and contrast the effects of 3 vasodilators on RV performance and central hemodynamic function. Nitroglycerin significantly decreased mean right atrial pressure, RV end-diastolic volume index, mean pulmonary artery pressure, cardiac index, and arterial oxygen tension, but did not affect pulmonary vascular resistance index and increased RV ejection fraction. Nitroprusside had similar effects on mean right atrial pressure, RV end-diastolic volume index, mean pulmonary artery pressure, cardiac index, and arterial oxygen tension, but also mildly decreased pulmonary vascular resistance index and did not alter RV ejection fraction. In contrast, hydralazine decreased pulmonary vascular resistance index and increased cardiac index and RV ejection fraction. The increase in ejection fraction correlated well with the decrease in pulmonary vascular resistance. These data suggest that in patients with mild to moderate secondary pulmonary hypertension, acute administration of hydralazine results in a substantial improvement in RV performance by virtue of decreasing pulmonary vascular resistance. In contrast, nitroglycerin and nitroprusside demonstrate predominant effects that reduce preload, cardiac index, and arterial oxygen tension. Based on these data, afterload reduction with vasodilators such as hydralazine may be potentially useful in selected patients with pulmonary disease and secondary pulmonary hypertension and appear preferable to agents that primarily reduce preload. Further long-term studies are necessary to establish therapeutic efficacy.

Effect of nitroglycerin on pulmonary perfusion distribution and gas exchange of normal subjects

In eight healthy subjects we assessed the effects of 3 mg sublingual nitroglycerin on lung distribution of ventilation and perfusion using 133Xe (sitting, supine and lateral decubitus) and on alveolo-arterial O2 and CO2 partial pressure differences [(PAO2-PaO2), (PaCO2-PACO2)] and physiological dead space to tidal volume ratio (VD/VT) (sitting). In all studied positions, nitroglycerin induced a significant decrease in uppermost perfusion indices, and a significant increase in dependent perfusion indices, without changing the distribution of ventilation. Significant increases in (PaCO2-PACO2) and VD/VT were observed up to 60 min after nitroglycerin. No changes in (PAO2-PaO2) occurred, except for a transient decrease due to transient hyperventilation following nitroglycerin. The redistribution of pulmonary perfusion after nitroglycerin may be attributed to the passive effects of lowered pulmonary vascular pressures, and to possible action on extra-alveolar vessels. The evolution of the indices of pulmonary gas exchange is compatible with the observed redistribution of ventilation/perfusion relationships.

Intravenous nitroglycerin during surgery for coronary artery disease

Intravenous infusions of nitroglycerin decreased systemic systolic, pulmonary systolic and wedge pressures in β-blocked patients anaesthetised for coronary artery surgery with high dose of fentanyl without changing heart rate, diastolic pressure, or cardiac index, thus leading to an improvement in endocardial viability ratio.

The use of a nitroglycerin bolus to abort an acute myocardial ischaemic episode is described.

Effect of nitroglycerin ointment on hemodynamics in patients with mitral insufficiency

A reduction in impedance or afterload produces beneficial hemodynamic effects in patients with mitral regurgitation. This mechanism has been studied via intravenous infusion of nitroprusside, phentolamine, and hydralazine. But there is little information on the effect of nitroglycerin ointment in patients with mitral insufficiency. Thus 6 patients with mitral insufficiency underwent right and left heart catheterization. After the control hemodynamic measurements were recorded, a 2 1/2-inch strip of 2% nitroglycerin ointment was applied to the chest for half an hour. Pressure recordings and cardiac output were then repeated. The control cardiac index fell from 2.79 to a treatment value of 2.05 L/min/m2 (P < 0.01), while the stroke index also decreased from 29 to 22 ml/beat/m2 (P < 0.05). There was a nonsignificant increase in peripheral resistance. Thus nitroglycerin ointment can be detrimental when given to patients with mitral insufficiency.

Mechanism of nitroglycerin-induced hypoxemia

We and others have previously demonstrated a consistent significant decline in arterial oxygen tension (PaO2) after sublingual nitroglycerin in premedicated and unpremedicated patients both with and without coronary artery disease and/or obstructive ventilatory disease. Thus, in our 19 patients, PaO2 fell by an average of 17% (12 mm Hg), mean systemic arterial pressure by 19% (17 mm Hg), pulmonary arterial pressure by 38% (6 mm Hg), pulmonary arterial occlusive pressure by 62% (5.3 mm Hg), and cardiac index by 16% (0.37 liter/min/m2) [P less than 0.001 for each] after nitroglycerin. Previous experimental studies suggest that the mechanism for the reduction of PaO2 may be relief of hypoxic pulmonary vasoconstriction with an increase in perfusion to poorly ventilated or nonventilated regions of the lungs. To examine this possibility, pulmonary vasodilatation was precluded by administration of a pulmonary vasoconstrictor (phenylephrine) simultaneously with nitroglycerin in nine patients with coronary artery disease. No significant change was observed in systemic or pulmonary arterial pressure, pulmonary arterial occlusive pressure, or systemic and pulmonary vascular resistance, and PaO2 did not decline. In ten other patients with coronary artery disease, the intrapulmonary right-to-left shunt fraction was determined before and after sublingual nitroglycerin; only a minimal increase in shunt fraction of 1.4% was observed, quantitatively insufficient to account for the observed decline in PaO2, thus excluding a predominant effect of nitroglycerin on nonventilated alveoli as a cause of the hypoxemia. We conclude that the reduction of PaO2 after nitroglycerin administration is attributable to pulmonary vasodilatation with a relative increase in perfusion of poorly ventilated lung units.