The lungs as receptor sites for cardiovascular regulation

High frequency jet ventilation (HFJV) has no better haemodynamic tolerance than controlled mechanical ventilation (CMV) in cardiogenic shock

Six patients with acute myocardial infarction (AMI) complicated by cardiogenic shock were studied in order to compare the haemodynamic tolerance of controlled mechanical ventilation (CMV) and high frequency jet ventilation (HFJV). The comparative analysis of the two techniques was performed with the same levels of PaO2 (CMV: 101 +/- 13 mmHg; HFJV: 104.2 +/- 14 p = ns); and PaCO2 (CMV: 37 +/- 1.7; HFJV: 35.7 +/- 1.4 p = ns). In this situation the values of mean airway pressure (Paw) did not differ significantly (CMV: 13 +/- 3 cm H2O; HFJV: 12.6 +/- 3.8 cm H2O) and no statistically significant difference in haemodynamic values was observed. These results demonstrate that in patients with cardiogenic shock, there is no difference between HFJV and CMV in terms of haemodynamic tolerance. Because of the more difficult clinical management of HFJV, this technique does not seem indicated as ventilatory support in patients with cardiogenic shock states.

A model for variability in arteriographic reading

We propose a class of models for the joint cumulative distribution function (c.d.f.) of the values of two independent readings of percentage stenosis from a coronary arteriography. We show that these models are identifiable and that a certain subclass has unique consistent estimators for the parameters in question. We obtain these estimates for a data set from a substudy of the Coronary Artery Surgery Study (CASS).

Institutional differences in therapeutic decision making in the Coronary Artery Surgery Study (CASS)

This article examines institutional differences in therapeutic decision making in the Coronary Artery Surgery Study (CASS). The initial decision to use medical therapy or coronary artery bypass surgery for coronary artery disease is studied. Data from the CASS registry and a survey of CASS principal investigators were used to examine the effects of institutional characteristics, individual physician characteristics, and decision making responsibility on the recommended therapy, the actual therapy, and the ratio of the observed to expected number of surgeries. The results indicated that the experience and involvement of the surgeon in the decision making process were related to actual and recommended rates of surgery. The percentage of urgent transfers from other hospitals and the percentage of surgical referrals to outside hospitals were related to the ratio of the observed to expected numbers of surgery, an adjusted rate of surgery. A major conclusion of this study is that despite the effects of certain institutional constructs, scientific criteria in the form of clinical and angiographic data are the most important determinants of whether a patient receives coronary artery bypass surgery.

Sympathetic nerve activity and central haemodynamics during mechanical ventilation with positive end-expiratory pressure in rats

The aim of this study was to examine the effects of mechanical ventilation with increasing levels of positive end-expiratory pressure (PEEP) on sympathetic nerve activity (SNA), cardiac output (CO), stroke volume (SV), heart rate (HR), central blood volume (CBV), total peripheral resistance (TPR), mean arterial pressure (MAP), pulse pressure (PP) and right and left atrial transmural pressure in chloralose anaesthetized rats before and after vagotomy. Changing ventilatory pattern from spontaneous breathing (SB) to artificial ventilation with 10 cm H2O PEEP in intact animals caused a significant fall in CO, SV and CBV (42, 48 and 17%, respectively) and an increase in SNA, HR and TPR (90, 13 and 83%, respectively). The MAP increased slightly but significantly from 103 +/- 4 to 107 +/- 4 mmHg while PP decreased from 48 +/- 2 to 37 +/- 3, from spontaneous breathing (SB) to 10 cm H2O PEEP. Transmural left atrial pressure decreased significantly from 4.5 +/- 0.3 to 3.0 +/- 0.4 mmHg. After vagotomy, MAP and CO were significantly lower at 10 cm H2O PEEP and PP and SV were significantly lower at all levels of positive end-expiratory pressure than the corresponding prevagotomy values. In spite of a greater fall in MAP and PP during PEEP after vagotomy, the absolute and relative increase of SNA was significantly lower compared to corresponding prevagotomy values. We conclude that reflex cardiovascular adjustments elicited by ventilation with PEEP are not solely due to unloading of arterial baroreceptors as has been claimed by others. Unloading of cardiac receptors with tonically active inhibitory afferents in the vagi is probably also of great importance for the excitation of the sympathetic nervous system during mechanical ventilation with PEEP.

Assisted ventilation in patients with preexisting cardiopulmonary disease. The effect on systemic oxygen consumption, oxygen transport, and tissue perfusion variables

We have evaluated systemic oxygen consumption (VO2), systemic oxygen transport, and tissue perfusion variables in 30 patients with preexisting cardiac and underlying pulmonary disease during continuous positive-pressure ventilation and positive end-expiratory pressure [PEEP], during intermittent mandatory ventilation (IMV and PEEP), and during spontaneous ventilation (continuous positive airway pressure [CPAP]), with end-expiratory pressure held constant during all ventilatory modes. Using radionuclide angiography together with invasive determinations of pressure and flow, we also measured left and right ventricular ejection fractions and calculated the end-systolic (ESVI) and end-diastolic (EDVI) volume indices of both ventricles. We found that oxygen transport was significantly greater during CPAP (583 +/- 172 ml/min/M2)(mean +/- SD) than during either IMV and PEEP (543 +/- 151 ml/min/sq; p less than 0.01) or CPPV and PEEP (526 +/- 159 ml/min/M2; p less than 0.01); however, we found no significant change in systemic VO2 with conversion from CPPV and PEEP to CPAP. The increase in oxygen transport was related to a greater cardiac index and, more specifically, to a higher heart rate during CPAP (CPAP, 106 +/- 16 beats per minute; CPPV and PEEP, 97 +/- 14 beats per minute) (p less than 0.01). Enhanced oxygen transport during CPAP was also associated with an increase in mixed venous oxygenation and a decrease in arterial lactate. Although neither the mean left ventricular EDVI nor ESVI changed from CPPV and PEEP to CPAP, the mean pulmonary capillary wedge pressure increased (CPPV and PEEP, 12 +/- 5 mm Hg; CPAP, 14 +/- 7 mm Hg) (p less than 0.01), suggesting the possibility of a decrease in left ventricular compliance with the spontaneous ventilatory mode. This study suggests that in the absence of ventilatory failure, spontaneous ventilation provides for better systemic oxygen transport and overall tissue perfusion than either controlled ventilation or IMV; however, this benefit of enhanced oxygen delivery with spontaneous ventilation may potentially be offset by a decrease in left ventricular compliance.

Surgical survival in the Coronary Artery Surgery Study (CASS) registry

The overall surgical survival data in the Coronary Artery Surgery Study (CASS) registry have not been published to date, pending the report of the randomized medical-surgical comparison (CASS randomized trial). Non-randomized surgical survival data from the CASS registry are given in this article. The overall medical survival data from the registry were reported previously as a natural history study. There were 8,991 patients in the registry portion of CASS who had primary isolated coronary artery bypass grafting and 8,971 with follow-up of more than 30 days. The 5-year survival for all 8,971 patients was 90%, and the operative mortality was 2.37%. Patients with left main coronary artery disease had an operative mortality of 3.84% and a 5-year survival of 85%, while patients with lesions in other vessels had an operative mortality of 2.12% and a 5-year survival of 91%. Among patients without left main coronary disease, the 5-year survival was 93% in those with single-vessel and 92% in those with double-vessel disease (operative mortality was 1.50% and 1.92%, respectively) and 88% in patients with triple-vessel disease (operative mortality was 2.62%; p = 0.009). When results for patients with left main coronary artery obstruction were compared with those for triple-vessel disease, the 5-year survival figures were 85% and 88%, respectively (p = 0.02) and the operative mortality, 3.84% and 2.62%, respectively (p = 0.03). Patients with normal or nearly normal left ventricular (LV) function (i.e., LV segmental wall motion scores ranging from 5 through 11) had a 5-year survival of 92% and an operative mortality of 1.97%. Patients with moderate impairment (LV score range, 12 through 16) had a 5-year survival of 80% and an operative mortality of 4.21%. In those with poor ventricular function (LV score of 17 or greater), the 5-year survival was 65% and the operative mortality was 6.21%. The difference in survival among the three groups was significant (p less than 0.0001). Of 29 variables used in a stepwise Cox regression analysis, LV wall motion score, congestive heart failure score, age, number of operable vessels, smoking history, LV end-diastolic pressure, and percent of left main coronary artery stenosis were found to have a significant effect on long-term survival (excluding 30-day mortality), and these variables plus surgical priority and height influenced surgical mortality. When height was used in the Cox proportional hazards model, female sex was no longer a significant variable.

The decision concerning coronary angiography in patients with chest pain. A cost-effectiveness analysis

We examined the decision whether to perform coronary angiography (followed by bypass surgery if appropriate findings are present) in middle-aged men who have chest pain and have undergone exercise tolerance testing (ETT). We developed a model of this decision that combines data from a variety of sources and selects the optimal strategy based on health outcome and, if desired, monetary cost. The analysis supports the following conclusions: for patients with nonspecific chest pain or atypical angina, the ETT provides useful information concerning the decision; furthermore, the number of millimeters of ST-segment depression above which angiography should be performed depends on coronary risk factors and pain severity. A normal ETT is insufficient evidence to exclude coronary angiography for patients with typical angina, provided that one is willing to expand resources for health benefits at levels comparable to those for other accepted medical practices. If monetary considerations are excluded, the preceding statement concerning ETT and angiography also holds for patients with atypical angina and for those with nonspecific pain and advanced risk factors. These last two conclusions suggest that ETT is not useful in guiding management decisions concerning coronary angiography in patients at high enough risk of coronary artery disease on the basis of symptoms and risk profile.

Comparison of coronary artery bypass surgery and medical therapy in patients 65 years of age or older. A nonrandomized study from the Coronary Artery Surgery Study (CASS) registry

We compared the results of coronary artery bypass surgery with those of medical therapy alone in 1491 nonrandomized patients 65 years of age or older. Cumulative survival at six years (adjusted for major differences in important base-line characteristics) was 79 per cent in the surgical group and 64 per cent in the medical group (P less than 0.0001). At five years, chest pain was absent in 62 per cent of the surgical group and 29 per cent of the medical group (P less than 0.0001). Analysis by the Cox proportional-hazards model suggested an independent beneficial effect of surgery on survival (P less than 0.0001). Patients were divided into risk quartiles on the basis of preoperative predictors of survival identified by the Cox model. Surgical benefit was greatest in "high-risk" patients (those in the two quartiles containing patients with the poorest prognosis). Among 234 "low-risk" patients with mild angina, relatively good ventricular function, and no left main coronary artery disease, there was no survival difference between those treated medically and those treated surgically. We conclude that in specific higher-risk subsets of non-randomized patients 65 years of age or older, coronary bypass surgery appeared to improve survival and symptoms in comparison with medical therapy alone. These conclusions must be tempered by consideration of the limitations of nonrandomized studies, particularly since patients in the two treatment groups differed substantially with regard to important base-line characteristics.

A randomized trial of coronary artery bypass surgery. Survival of patients with a low ejection fraction

The Coronary Artery Surgery Study (CASS) was designed to compare medical and surgical treatment of selected patients with chronic, stable coronary artery disease. This report concerns a subset of patients with reduced ventricular function. Of 780 patients randomly assigned to medical or surgical treatment, 160 had ejection fractions above 0.34 but below 0.50 at base line and have been followed for an average of seven years. Eighty-two patients were assigned to medical therapy, and 78 to surgery; the two groups were comparable at base line with regard to prognostically important variables. At seven years, 84 per cent of patients in the surgical group were alive, as compared with 70 per cent of the medical group (P = 0.01). Nearly half the patients with impaired ventricular function had triple-vessel disease at entry; at seven years, observed survival in this group was 88 and 65 per cent for those assigned to surgical and medical treatment, respectively (P = 0.009). Survival of patients with single-vessel or double-vessel disease was similar in the two treatment groups. We conclude that patients with triple-vessel disease and ejection fractions higher than 0.34 but lower than 0.50 appear to have improved seven-year survival with elective bypass surgery.

Split medulla preparation in the cat: arterial chemoreceptor reflex and respiratory modulation of the renal sympathetic nerve activity

The study was undertaken in order to assess the changes in sympathetic output in a split medulla preparation of the cat which, as shown earlier, has impaired respiratory rhythm generation. The effects of medullary midsagittal sections on renal sympathetic nerve firing were investigated in chloralose anesthetized, paralyzed and artificially ventilated cats. Recordings of phrenic and recurrent laryngeal nerve activity served as indices of central respiratory rhythm generation. Sections, 5 mm deep from the dorsal medullary surface and extending 6 mm rostrally and 3 mm caudally to the obex, did not produce any significant changes in heart rate, blood pressure or tonic renal sympathetic nerve firing levels. They decreased or abolished, however, the respiratory rhythmicity in renal sympathetic nerve which paralleled the reduction of inspiratory discharges in phrenic and recurrent laryngeal nerves, and abolished the carotid body chemoreceptor-sympathetic reflex. The inspiratory activity remaining after the sections could still be enhanced by chemoreceptor stimulation. The inhibitory baroreceptor and pulmonary stretch receptor sympathetic reflexes, and the central excitatory effect of CO2 on renal sympathetic nerve firing were not altered. The effects of electrical stimulation within the midsagittal plane of the medulla have shown that descending pathways from the medullary inspiratory neurons (or their medullary collaterals) do not participate in the facilitation of spinal preganglionic neurons during inspiration and in relaying the pulmonary stretch receptor inhibitory sympathetic reflex. A region located close to the obex was identified from which excitatory responses in renal sympathetic nerves, compatible with the response obtained by carotid sinus nerve stimulation, could be evoked. It is concluded that a lesion in the midline of the lower medulla at the level of the obex selectively destroys cells or pathways which relay the carotid body chemoreceptor-sympathetic reflex.

Implications of precordial ST segment depression during acute inferior myocardial infarction. Arteriographic and ventriculographic correlations during the acute phase

Thirty two patients presenting with acute transmural inferior wall myocardial infarction underwent cardiac catheterisation and angiography within 12 hours of the onset symptoms. Twelve lead electrocardiograms performed within one hour of catheterisation showed ST segment depression in the anterior precordial leads in addition to inferior wall changes in 17 patients and no ST segment changes in the anterior leads in 15. When the clinical, arteriographic, and ventriculographic variables were compared between the two groups no significant differences were noted with regard to age, sex, risk factors for coronary disease, duration of symptoms before angiography, Killip class, number of inferior leads with ST segment elevation, or initial serum creatine kinase activity. The extent of coronary artery disease as well as the prevalence of severe disease in the left anterior descending artery were similar for both groups. Biplane left ventriculography showed no significant differences between the two groups with regard to global ejection fraction or to the prevalence of posterolateral or anterior segmental wall motion abnormalities.

Myocardial infarction and mortality in the coronary artery surgery study (CASS) randomized trial

The long-term benefit of coronary bypass surgery in terms of longevity and prevention of major ischemic events in patients who have mild angina is not well defined. The randomized Coronary Artery Surgery Study (CASS) was designed to evaluate this issue; it consists of 780 patients who were considered operable and who had mild stable angina pectoris or who were free of angina after infarction. As a result of the randomization process there were no significant differences in base-line variables between patients randomly assigned to medical and to surgical therapy. The likelihood of death in the five-year period after randomization was only 8 per cent in the medical cohort, as compared with 5 per cent in the surgical cohort (not significant). The likelihood of nonfatal Q-wave myocardial infarction was 11 and 14 per cent, respectively (not significant). The five-year probability of remaining alive and free of infarction was 82 per cent in the patients assigned to medical therapy and 83 per cent in the patients assigned to surgery (not significant). There were no statistically significant differences in the survival rate or in the myocardial-infarction rate between subgroups of patients randomly assigned to medical and to surgical therapy when they were analyzed according to initial group assignment, number of diseased vessels, or ejection fraction. Therefore, as compared with medical therapy, coronary bypass surgery appears neither to prolong life nor to prevent myocardial infarction in patients who have mild angina or who are asymptomatic after infarction in the five-year period after coronary angiography.

Reticular formation of the lower brainstem. A common system for cardiorespiratory and somatomotor functions: discharge patterns of neighboring neurons influenced by cardiovascular and respiratory afferents

Experiments were done in dogs with chloralose-urethane anesthesia. Long-lasting extracellular recordings were made from the medial parts of the reticular formation of the lower brainstem for up to 250 min. The study is based on reactions of 103 neurons. The activities of 2 or 3 neighbouring neurons recorded under identical conditions with one electrode or of neurons recorded with two electrodes at the same time could be changed regularly and synchronously by experimental changes of hemodynamic or ventilatory parameters. Action potentials were separated by amplitude discrimination. Rhythmic pulsatile modulations were proved to be present in 78% of all neurons by post-event-time histograms triggered by the R-wave of the ECG. In the 96 neurons tested 86% changed their activity when arterial pressure was raised by inflating a balloon in the abdominal aorta (79% decreased and 7% increased their activity). In post-event-time histograms triggered by the start of inspiration, 83% of the neurons showed modulations of their activity with respiratory rhythm. Experimental lung inflation decreased the activity in 75% of the tested neurons, while experimental lung deflation activated 47% of the tested neurons. Stimulation of arterial chemoreceptors activated 77% of the tested neurons. It was thus demonstrated that receptors in the cardiovascular and respiratory systems exert an influence on nearly all neurons from which recordings were made in that part of the reticular formation. Arterial baroreceptors and lung stretch receptors revealed a generalized depressing effect on the neuronal activity while chemoreceptors exert a generalized augmenting effect. At different times of recording these neurons did not always react to the same extent to comparable stimulations of afferents.

Reproducibility of coronary arteriographic reading in the coronary artery surgery study (CASS)

Eight hundred seventy arteriograms from the Coronary Artery Surgery Study (CASS) were independently read by readers at two different clinics to evaluate the reproducibility of the interpretation of coronary arteriograms. Among proximal segments, the interpretation of lesions of the left main coronary artery were the least reproducible, P less than .02. When one angiographer reads a stenosis of 50% or more in the left main coronary artery, it is estimated that a second reader will report no lesion 18.6% of the time. In 94.7% of the films, the number of significantly (greater than or equal to 70% stenosis) diseased vessels was the same for both readers (72.1%) or differed by one vessel (22.6%). The reproducibility of interpretation of films of good or acceptable quality or completeness was better than the reproducibility of readings of arteriograms judged to be of poor quality or incomplete studies. The mean absolute difference between readings of the percent stenosis decreased over the time of the patient enrollment, 1975 to 1978. This may have resulted from major collaborative efforts made during the course of the study to improve the quality of angiography and to standardize the reading of the cine films.

The brain-stem projections of pulmonary stretch afferent neurones in cats and rabbits

1. Micro-electrode recordings were made from slowly adapting pulmonary stretch afferents within the nodose ganglia of cats and rabbits. Recordings sites were distributed throughout the ganglia. 2. The projections of these afferents to the medulla oblongata were studied by antidromic stimulation. 'Point' and 'Field' type depth--threshold curves were interpreted as corresponding to stimulation of the main afferent axons and its branches, respectively. Increases in antidromic latency in conjunction with 'field' contours was additional evidence in support of this interpretation. 3. In cats, most (six out of seven) afferents had extensive branches, and probably also terminations, within the medial subnucleus of the ipsilateral nucleus tractus solitarius (n.t.s.). Two of these, plus one other afferent, also had projections to the lateral and ventrolateral subnuclei. 4. In rabbits the projections of such afferents were similar, i.e. mainly to the medial subnucleus of the n.t.s. (eight out of eleven) but also extending into the nucleus alaris, and occasionally to lateral and ventrolateral subnuclei (two out of eleven) or to both regions (one out of eleven). 5. Branching of single afferents was seen to occur over up to 3 mm of the rostro-caudal extent of the intermediate region of the n.t.s. The significance of the observations is discussed.