Safer paediatric surgical teams: A 5-year evaluation of crew resource management implementation and outcomes

Objective

Evaluate longitudinal changes in technical and non-technical skills (teamwork, situation monitoring, communication and leadership), safety culture, and clinical outcomes before and after implementation of a crew resource management (CRM) safety program.

Design

A multi-level prospective single case study in accordance with the SQUIRE-guidelines for reporting quality improvement efforts.

Setting

Large university paediatric surgical service.

Participant(s)

All 153 managers and staff.

Interventions

Training of staff in CRM, systematic risk assessments, and the redesign of work practices captured and reinforced through the development, implementation and refinement of SOPs.

Main Outcome Measure(s)

Data were collected related to: 1) Relevance of CRM training (survey), 2) Safety culture (survey), 3) Team behaviours in clinical practice (non-participatory observations with MedPACT protocol) and 4) Effects on perioperative care for laparoscopic appendectomies-a representative and frequently performed surgical procedure (electronic medical records and administrative data for length of stay, unplanned readmissions and returns to the Operating Room).

Results

Non-technical skills, the use of safety tools, as well as adherence to guidelines for appendectomies all improved significantly over time. Significant safety culture improvements were found in teamwork across and within units, supervisors' expectations and actions, non-punitive response to adverse events, and perceptions of overall patient safety. Unplanned readmissions following appendectomy declined significantly.

Conclusions

Implementation of a comprehensive CRM program including associated safety tools created sustained adherence to new work practices and improved non-technical and technical skills, surgical outcomes and safety culture.

Contextual adaptation of the Personnel Evaluation Standards for assessing faculty evaluation systems in developing countries: the case of Iran

BACKGROUND

Faculty evaluations can identify needs to be addressed in effective development programs. Generic evaluation models exist, but these require adaptation to a particular context of interest. We report on one approach to such adaptation in the context of medical education in Iran, which is integrated into the delivery and management of healthcare services nationwide.

METHODS

Using a triangulation design, interviews with senior faculty leaders were conducted to identify relevant areas for faculty evaluation. We then adapted the published checklist of the Personnel Evaluation Standards to fit the Iranian medical universities' context by considering faculty members' diverse roles. Then the adapted instrument was administered to faculty at twelve medical schools in Iran.

RESULTS

The interviews revealed poor linkages between existing forms of development and evaluation, imbalance between the faculty work components and evaluated areas, inappropriate feedback and use of information in decision making. The principles of Personnel Evaluation Standards addressed almost all of these concerns and were used to assess the existing faculty evaluation system and also adapted to evaluate the core faculty roles. The survey response rate was 74%. Responses showed that the four principles in all faculty members' roles were met occasionally to frequently. Evaluation of teaching and research had the highest mean scores, while clinical and healthcare services, institutional administration, and self-development had the lowest mean scores. There were statistically significant differences between small medium and large medical schools (p < 0.000).

CONCLUSION

The adapted Personnel Evaluation Standards appears to be valid and applicable for monitoring and continuous improvement of a faculty evaluation system in the context of medical universities in Iran. The approach developed here provides a more balanced assessment of multiple faculty roles, including educational, clinical and healthcare services. In order to address identified deficiencies, the evaluation system should recognize, document, and uniformly reward those activities that are vital to the academic mission. Inclusion of personal developmental concerns in the evaluation discussion is essential for evaluation systems.

Military aviators with mitral valve prolapse: long-term follow-up and aeromedical endpoints

INTRODUCTION

Mitral valve prolapse (MVP) is a disqualifying condition for USAF aviators. Trained USAF aviators, and in recent years flying training applicants, may be granted waiver for initial or continued flying duties following extensive, periodic evaluation. This study examines the usefulness of the various tests performed in that evaluation process and provides long-term follow-up from 404 USAF flyers with MVP.

METHODS

We retrospectively reviewed 2-dimensional echocardiography, Holter monitoring, treadmill exercise, thallium imaging, coronary fluoroscopy, cardiac catheterization, and centrifuge testing results from 404 military aviators evaluated at the Aeromedical Consultation Service between 1 January 1972 and 31 October 1993. Follow-up was achieved through questionnaires (91%) and death certificates, etc.

RESULTS

Mean follow-up was 8.6 yr (range 1-21 yr). Age at study entry was 21 to 64 yr (mean = 36 yr). The occurrence rate for suddenly incapacitating events (sudden cardiac death, syncope, pre-syncope, and cerebral ischemic episodes) was 0.32%/yr.

CONCLUSIONS

Echocardiographic MVP in military aviators is associated with a low but statistically increased prevalence of "incapacitating" aeromedical events. Univariate predictors of adverse outcome included study entry with an enlarged left ventricle or left atrium, cardiovascular symptoms or findings, or MVP with thickened leaflets. Evaluation of coronary artery disease (CAD) in this population, absent specific indicators of CAD risk, is not indicated.

The impact of aviation-based teamwork training on the attitudes of health-care professionals

BACKGROUND

Both the Institute of Medicine and the Agency for Healthcare Research and Quality suggest patient safety can be enhanced by implementing aviation Crew Resource Management (CRM) in health care. CRM emphasizes six key areas: managing fatigue, creating and managing teams, recognizing adverse situations (red flags), cross-checking and communication, decision making, and performance feedback. This study evaluates participant reactions and attitudes to CRM training.

STUDY DESIGN

From April 22, 2003, to December 11, 2003, clinical teams from the trauma unit, emergency department, operative services, cardiac catheterization laboratory, and administration underwent an 8-hour training course. Participants completed an 11-question End-of-Course Critique (ECC), designed to assess the perceived need for training and usefulness of CRM skill sets. The Human Factors Attitude Survey contains 23 items and is administered on the same day both pre- and posttraining. It measures attitudinal shifts toward the six training modules and CRM.

RESULTS

Of the 489 participants undergoing CRM training during the study period, 463 (95%) completed the ECC and 338 (69%) completed the Human Factors Attitude Survey. The demographics of the group included 288 (59%) nurses and technicians, 104 (21%) physicians, and 97 (20%) administrative personnel. Responses to the ECC were very positive for all questions, and 95% of respondents agreed or strongly agreed CRM training would reduce errors in their practice. Responses to the Human Factors Attitude Survey indicated that the training had a positive impact on 20 of the 23 items (p < 0.01).

CONCLUSIONS

CRM training improves attitudes toward fatigue management, team building, communication, recognizing adverse events, team decision making, and performance feedback. Participants agreed that CRM training will reduce errors and improve patient safety.

An Intravenous Medication Safety System

Improving medication safety at the point of care--particularly for high-risk drugs--is a major concern of nursing administrators. The medication errors most likely to cause harm are administration errors related to infusion of high-risk medications. An intravenous medication safety system is designed to prevent high-risk infusion medication errors and to capture continuous quality improvement data for best practice improvement. Initial testing with 50 systems in 2 units at Vanderbilt University Medical Center revealed that, even in the presence of a fully mature computerized prescriber order-entry system, the new safety system averted 99 potential infusion errors in 8 months.

A novel angiotensin II type 2 receptor signaling pathway: possible role in cardiac hypertrophy

We describe a novel signaling mechanism mediated by the G-protein-coupled receptor (GPCR) angiotensin II (Ang II) type 2 receptor (AT(2)). Yeast two-hybrid studies and affinity column binding assay show that the isolated AT(2) C-terminus binds to the transcription factor promyelocytic zinc finger protein (PLZF). Cellular studies employing confocal microscopy show that Ang II stimulation induces cytosolic PLZF to co-localize with AT(2) at the plasma membrane, then drives AT(2) and PLZF to internalize. PLZF slowly emerges in the nucleus whereas AT(2) accumulates in the perinuclear region. Nuclear PLZF binds to a consensus sequence of the phosphatidylinositol-3 kinase p85 alpha subunit (p85 alpha PI3K) gene. AT(2) enhances expression of p85 alpha PI3K followed by enhanced p70(S6) kinase, essential to protein synthesis. An inactive mutant of PLZF abolishes this effect. PLZF is expressed robustly in the heart in contrast to many other tissues. This cardiac selective pathway involving AT(2), PLZF and p85 alpha PI3K may explain the absence of a cardiac hypertrophic response in AT(2) gene-deleted mice.

Do Women Simply Complain More? National Patient Injury Claims Data Show Gender and Age Differences

The Swedish Counties Mutual Insurance (LOF) owns and operates the Swedish Patient Insurance Company, (PSR) a no-blame insurance system that compensates patients for injuries that result from errors in medical practice. We combined malpractice claims data (from PSR) with national hospital discharge registry data (National Board of Health and Welfare-Socialstyrelsen) and determined Swedish inpatient malpractice claims rates for the years 1996-2000. Women have higher claims rates than men, but their claims are adjudicated as valid more often than men's claims. The data are consistent with other lines of evidence suggesting poorer quality of care for women, e.g., heart disease, kidney disease, and cancer. Middle-aged (40- to 59-year-old) patients file malpractice claims at almost twice the national rate, whereas patients younger than 19 years and older than 80 years of age file at significantly below the average rate. Differences in claims rates have major financial and quality of care implications. Further studies are needed.

Targeted deletion of angiotensin II type 2 receptor caused cardiac rupture after acute myocardial infarction

BACKGROUND

Accumulating evidence has suggested that the cardiac renin-angiotensin system is activated during the remodeling process after myocardial infarction (MI). Although 2 types of angiotensin II receptors (AT(1) and AT(2)) are upregulated in the infarcted tissue, the contribution of AT(2) to the subsequent fibrogenetic phase of wound healing is less certain. This study was conducted to evaluate the role of AT(2) in wound healing after MI using an in vivo intervention study in mice with MI.

METHODS AND RESULTS

We examined myocardial hypertrophy, cardiac fibrosis, and morphological evidence of fibrillar collagen accumulation at the infarcted and noninfarcted regions in male mice lacking the AT(2) receptor (Agtr2-/Y) and age-matched wild-type (WT) animals. Of the Agtr2-/Y mice, 63.6% died of cardiac rupture, whereas 23.5% of the WT mice died of the same cause within 1 week. The extent of fibrosis and that of collagen gene expression in Agtr2-/Y mice were significantly reduced compared with WT mice at 1 week after coronary ligation. Furthermore, MI resulted in a marked increase in the prostaglandin E(2) (PGE(2)) level at 4 days after surgery in Agtr2-/Y mice. In WT mice, the PGE(2) level was also elevated after MI but to a significantly lesser extent than in Agtr2-/Y mice.

CONCLUSIONS

A chronic loss of AT(2) by gene targeting prevented the collagen deposition and caused cardiac rupture. The markedly elevated PGE(2) may be a mechanism that inhibits collagen synthesis in the infarcted region of Agtr2-/Y mice.

Human muscle sympathetic nerve activity and plasma noradrenaline kinetics in space

Astronauts returning from space have reduced red blood cell masses, hypovolaemia and orthostatic intolerance, marked by greater cardio-acceleration during standing than before spaceflight, and in some, orthostatic hypotension and presyncope. Adaptation of the sympathetic nervous system occurring during spaceflight may be responsible for these postflight alterations. We tested the hypotheses that exposure to microgravity reduces sympathetic neural outflow and impairs sympathetic neural responses to orthostatic stress. We measured heart rate, photoplethysmographic finger arterial pressure, peroneal nerve muscle sympathetic activity and plasma noradrenaline spillover and clearance, in male astronauts before, during (flight day 12 or 13) and after the 16 day Neurolab space shuttle mission. Measurements were made during supine rest and orthostatic stress, as simulated on Earth and in space by 7 min periods of 15 and 30 mmHg lower body suction. Mean (+/- S.E.M.) heart rates before lower body suction were similar pre-flight and in flight. Heart rate responses to -30 mmHg were greater in flight (from 56 +/- 4 to 72 +/- 4 beats min(-1)) than pre-flight (from 56 +/- 4 at rest to 62 +/- 4 beats min(-1), P < 0.05). Noradrenaline spillover and clearance were increased from pre-flight levels during baseline periods and during lower body suction, both in flight (n = 3) and on post-flight days 1 or 2 (n = 5, P < 0.05). In-flight baseline sympathetic nerve activity was increased above pre-flight levels (by 10-33 %) in the same three subjects in whom noradrenaline spillover and clearance were increased. The sympathetic response to 30 mmHg lower body suction was at pre-flight levels or higher in each subject (35 pre-flight vs. 40 bursts min(-1) in flight). No astronaut experienced presyncope during lower body suction in space (or during upright tilt following the Neurolab mission). We conclude that in space, baseline sympathetic neural outflow is increased moderately and sympathetic responses to lower body suction are exaggerated. Therefore, notwithstanding hypovolaemia, astronauts respond normally to simulated orthostatic stress and are able to maintain their arterial pressures at normal levels.

Transesophageal echocardiographic evaluation of baboons during microgravity induced by parabolic flight

The central cardiovascular responses to transient microgravity are not well understood. Theoretically, entrance into microgravity results in the loss of the hydrostatic pressure head and an increase in central venous pressure (CVP) as a consequence of augmented venous return. However, controversy exists regarding the time course and magnitude of cephalad blood volume shifts and its relationship to central atrial filling pressures. On the June 1991 STS 40 shuttle mission, pre-launch echocardiograms suggested changes in cardiac dimensions occurred while the astronauts were in the supine, feet-up position. Furthermore, a CVP line in an astronaut (n=1) demonstrated an unexpected abrupt decrease in CVP during orbital insertion. In April 1991, our laboratory performed Doppler echocardiography in 6 normal human volunteers during parabolic flight. Increases in right ventricular velocities reflecting a central shift of blood volume was demonstrated in subjects examined in the sitting position. However, test subjects examined in the horizontal positions had no significant rise in Doppler velocities. In addition, Latham et al noted variable central cardiovascular responses in chronically instrumented baboons during early microgravity. Transthoracic echocardiography (TTE) is a feasible method to noninvasively examine cardiac anatomy during parabolic flight. However, transducer placement on the chest wall is very difficult to maintain during transition to microgravity. In addition, TTE requires the use of low frequency transducers (2.5 MHz) which limits resolution. Transesophageal echocardiography (TEE) is an established imaging technique which obtains echocardiographic information from the esophagus. It is a safe procedure and provides higher quality images of cardiac structures than obtained with TTE. Since there are no interposed structures between the esophagus and the heart, higher frequency transducers can be used and resolution is enhanced. With TEE, a flexible transducer tip permits contact with the esophageal mucosa, allowing for consistent imaging. This study was designed to determine whether TEE was feasible to perform during parabolic flight and to determine whether acute central volume responses occur in acute transition to zero gravity (0G) by direct visualization of the cardiac chambers.

Stroke volume in-vivo using multiple 2D echo views from one echo window

We recently validated in-vitro a new mathematical approach to echocardiographic volume calculation. With this method all echo views are acquired from one point as the transducer is tilted. The angle of tilt of the transducer must be measured. A tilt frame was designed for use in-vivo that does not interfere with imaging. The method was then tested in-vivo by comparing echocardiographic stroke volume with stroke volume determined by the acetylene rebreathing technique. Normal subjects were studied with either lower body negative pressure or continuous isoproterenol infusion. The regression line was Echo SV=-19.7 + 1.2*Acet SV, with R=0.80, SEE=17.1, MPE=17%. We conclude that this is an accurate, non-geometric method for ventricular volume calculation.

Simplified right ventricular volume algorithm using one digitized view and transducer tilt angle

We recently described a technique for determining in-vitro right ventricular volume from multiple two-dimensional echocardiographic views taken at sequential angles. The product of sectional area and center of mass for each view (U) is integrated over the angle of tilt of the transducer to give volume. We now note that the plot of U vs. angle is almost triangular when the echoes are taken from the short axis position. The maximal U value (the vertex of the triangle) and the total angle span (the base) are then used in the equation (maximal U x total angle span)/2 to calculate volume. This new approximation provides an excellent correlation with actual volumes. We conclude that the triangular approximation provides accurate in-vitro estimates of right ventricular volume in normal human hearts.

Angiotensin II type 2 receptor is essential for left ventricular hypertrophy and cardiac fibrosis in chronic angiotensin II-induced hypertension

BACKGROUND

The roles of angiotensin II (Ang II) in the regulation of heart function under normal and pathological conditions have been well documented. Although 2 types of Ang II receptor (AT(1) and AT(2)) are found in various proportions, most studies have focused on AT(1)-coupled events. In the present study, we examined the hypothesis that signaling by AT(2) is important to the development of left ventricular hypertrophy and cardiac fibrosis by Ang II infusion in mice lacking the AT(2) gene (Agtr2-/Y).

METHODS AND RESULTS

Male Agtr2-/Y and age-matched wild-type (WT) mice were treated long-term with Ang II, infused at a rate of 4.2 ng. kg(-1). min(-1) for 3 weeks. Ang II elevated systolic blood pressure to comparable levels in Agtr2-/Y and WT mice. WT mice developed prominent concentric cardiac hypertrophy, prominent fibrosis, and impaired diastolic relaxation after Ang II infusion. In contrast, there was no cardiac hypertrophy in Agtr2-/Y mice. Agtr2-/Y mice, however, did not show signs of heart failure or impairment of ventricular relaxation and only negligible fibrosis after Ang II infusion. The absence of fibrosis may be a clue to the absence of impairment in ventricular relaxation and account for the normal left ventricular systolic and diastolic performances in Agtr2-/Y mice.

CONCLUSIONS

Chronic loss of AT(2) by gene targeting abolished left ventricular hypertrophy and cardiac fibrosis in mice with Ang II-induced hypertension.

Effects of spaceflight on human calf hemodynamics

Chronic microgravity may modify adaptations of the leg circulation to gravitational pressures. We measured resting calf compliance and blood flow with venous occlusion plethysmography, and arterial blood pressure with sphygmomanometry, in seven subjects before, during, and after spaceflight. Calf vascular resistance equaled mean arterial pressure divided by calf flow. Compliance equaled the slope of the calf volume change and venous occlusion pressure relationship for thigh cuff pressures of 20, 40, 60, and 80 mmHg held for 1, 2, 3, and 4 min, respectively, with 1-min breaks between occlusions. Calf blood flow decreased 41% in microgravity (to 1.15 +/- 0.16 ml x 100 ml(-1) x min(-1)) relative to 1-G supine conditions (1.94 +/- 0.19 ml x 100 ml(-1) x min(-1), P = 0.01), and arterial pressure tended to increase (P = 0.05), such that calf vascular resistance doubled in microgravity (preflight: 43 +/- 4 units; in-flight: 83 +/- 13 units; P < 0.001) yet returned to preflight levels after flight. Calf compliance remained unchanged in microgravity but tended to increase during the first week postflight (P > 0.2). Calf vasoconstriction in microgravity qualitatively agrees with the "upright set-point" hypothesis: the circulation seeks conditions approximating upright posture on Earth. No calf hemodynamic result exhibited obvious mechanistic implications for postflight orthostatic intolerance.

Evidence for angiotensin II type 2 receptor-mediated cardiac myocyte enlargement during in vivo pressure overload

The pathophysiological roles of the angiotensin II type 2 receptor (AT(2)) in cardiac hypertrophy remain unclear. By the targeted deletion of mouse AT(2) we were able to prevent the left ventricular hypertrophy resulting from pressure overload, while cardiac contractile functions remained normal. This implies that AT(2) is a mediator of cardiac hypertrophy in response to increased blood pressure. The effects of AT(2) deletion were independent of activation of embryonic genes for cardiac hypertrophy. However, p70(S6k), one of the key factors in cardiac hypertrophy, was markedly and specifically reduced in the ventricles of Agtr2(-)/Y mice. We propose that p70(S6k) plays a major role in AT(2)-mediated ventricular hypertrophy. This article may have been published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

Alterations in the volume stimulus-renal response relationship during exposure to simulated microgravity

We measured central venous pressure (CVP), plasma volume (PV), urine volume rate (UVR), and circulating hormones (renin activity (PRA), vasopressin (AVP), atrial natriuretic peptide (ANP), and cortisol) before and after acute volume infusion (Dextran-40) to test the hypotheses that head-down tilt bedrest (HDT) caused (1) a resetting of the CVP operating point and (2) attenuated urine excretion. Six rhesus monkeys underwent two experimental conditions (HDT and control, each of 48 hour duration) with each condition separated by nine days of ambulatory activities to produce a cross-over counterbalance design. One test condition was continuous exposure to 10 degrees HDT and the second test condition was a control, defined as approximately 12-14 hours per day of 80 degrees head-up tilt and 10-12 hours prone. Following 48 hours of exposure to either test condition, 20-minute continuous infusion of Dextran-40 was administered. CVP in HDT was lower than the control condition. Similar elevations in CVP occurred 30 min post-infusion in both test conditions, and returned to pre-infusion baseline levels between 22 and 46 h post-infusion in both treatments. The UVR response during infusion was attenuated by HDT despite similar elevation in CVP. Elevation in ANP and reduction in PRA at the end of infusion were greater in Control compared to HDT. No differences between control and HDT were detected for AVP and cortisol responses to infusion. Since CVP returned to its pre-infusion levels following volume loading in HDT and control conditions, it appeared that the lower CVP may reflect a new operating point about which vascular volume is regulated. Further, attenuated ANP and PRA responses during vascular volume loading may contribute to depressed UVR in low gravity exposure.

Prehospital ECG monitoring of chest pain patients

Prehospital electrocardiograms (ECGs) have been shown to decrease the time from onset of pain to onset of treatment. They are obtained prior to treatment while the patient is likely to have his/her most intense pain. With paramedics initiating care in the field, patient assessments may be clinically different by the time the patient reaches the hospital. Thus, obtaining an ECG as early as possible during treatment could aid in the access to treatment for the few patients whose ECGs improve with prehospital care. We present a case in which the prehospital presentation was indicative of an acute myocardial infarction (MI), whereas the presentation to the hospital was not as clear-cut. The patient was taken immediately to the catheterization laboratory based on the prehospital findings and was found to have an acute MI that was treated. Laboratory findings indicated that there was a significant improvement in patient outcome based on this early treatment. This case further illustrates the role of a prehospital ECG.

Measurement of net whole-body transcapillary fluid transport and effective vascular compliance in humans

BACKGROUND

Net whole-body transcapillary fluid transport (TFT) between the circulation and the interstitial (extravascular) space may be calculated as: IV - deltaPV - UV - IL, where IV=infused or ingested volume (when applicable), deltaPV = change in plasma volume, UV=urine volume, and IL=insensible loss.

RESULTS

Infusion of 30 mL/kg isotonic saline over 25 minutes increased supine TFT from a basal capillary reabsorption of -106+/-24 mL/h (mean+/-SE) to a net filtration of 1,229+/-124 mL/h. One hour after infusion, reabsorption of -236+/-102 mL/h was seen, and control reabsorption levels returned by 3 hours. Four hours of 30 mm Hg lower body negative pressure (LBNP) elicited no net TFT, probably because of upper body reabsorptive compensation for lower body capillary filtration. When ingestion of 1 L of isotonic saline accompanied LBNP, filtration of 145+/-10 mL/h occurred. Reabsorption of extravascular fluid into the circulation always followed LBNP.

CONCLUSION

Application of this technique could aid understanding of physiologic conditions, experimental interventions, disease states, and therapies that cause or are influenced by fluid shifts between intravascular and interstitial compartments.

Evidence for increased cardiac compliance during exposure to simulated microgravity

We measured hemodynamic responses during 4 days of head-down tilt (HDT) and during graded lower body negative pressure (LBNP) in invasively instrumented rhesus monkeys to test the hypotheses that exposure to simulated microgravity increases cardiac compliance and that decreased stroke volume, cardiac output, and orthostatic tolerance are associated with reduced left ventricular peak dP/dt. Six monkeys underwent two 4-day (96 h) experimental conditions separated by 9 days of ambulatory activities in a crossover counterbalance design: 1) continuous exposure to 10 degrees HDT and 2) approximately 12-14 h per day of 80 degrees head-up tilt and 10-12 h supine (control condition). Each animal underwent measurements of central venous pressure (CVP), left ventricular and aortic pressures, stroke volume, esophageal pressure (EsP), plasma volume, alpha1- and beta1-adrenergic responsiveness, and tolerance to LBNP. HDT induced a hypovolemic and hypoadrenergic state with reduced LBNP tolerance compared with the control condition. Decreased LBNP tolerance with HDT was associated with reduced stroke volume, cardiac output, and peak dP/dt. Compared with the control condition, a 34% reduction in CVP (P = 0.010) and no change in left ventricular end-diastolic area during HDT was associated with increased ventricular compliance (P = 0.0053). Increased cardiac compliance could not be explained by reduced intrathoracic pressure since EsP was unaltered by HDT. Our data provide the first direct evidence that increased cardiac compliance was associated with headward fluid shifts similar to those induced by exposure to spaceflight and that reduced orthostatic tolerance was associated with lower cardiac contractility.

Maximal exercise performance after adaptation to microgravity

The cardiovascular system appears to adapt well to microgravity but is compromised on reestablishment of gravitational forces leading to orthostatic intolerance and a reduction in work capacity. However, maximal systemic oxygen uptake (Vo2) and transport, which may be viewed as a measure of the functional integrity of the cardiovascular system and its regulatory mechanisms, has not been systematically measured in space or immediately after return to Earth after spaceflight. We studied six astronauts (4 men and 2 women, age 35-50 yr) before, during, and immediately after 9 or 14 days of microgravity on two Spacelab Life Sciences flights (SLS-1 and SLS-2). Peak Vo2 (Vo2peak) was measured with an incremental protocol on a cycle ergometer after prolonged submaximal exercise at 30 and 60% of Vo2peak. We measured gas fractions by mass spectrometer and ventilation via turbine flowmeter for the calculation of breath-by-breath Vo2, heart rate via electrocardiogram, and cardiac output (Qc) via carbon dioxide rebreathing. Peak power and Vo2 were well maintained during spaceflight and not significantly different compared with 2 wk preflight. Vo2peak was reduced by 22% immediately postflight (P < 0.05), entirely because of a decrease in peak stroke volume and Qc. Peak heart rate, blood pressure, and systemic arteriovenous oxygen difference were unchanged. We conclude that systemic Vo2peak is well maintained in the absence of gravity for 9-14 days but is significantly reduced immediately on return to Earth, most likely because of reduced intravascular blood volume, stroke volume, and Qc.

Orthostatic intolerance after spaceflight

Orthostatic intolerance occurs commonly after spaceflight, and important aspects of the underlying mechanisms remain unclear. We studied 14 individuals supine and standing before and after three space shuttle missions of 9-14 days. After spaceflight, 9 of the 14 (64%) crew members could not complete a 10-min stand test that all completed preflight. Pre- and postflight supine hemodynamics were similar in both groups except for slightly higher systolic and mean arterial pressures preflight in the finishers [15 +/- 3.7 and 8 +/- 1.2 (SE) mmHg, respectively; P < 0.05]. Postflight, finishers and nonfinishers had equally large postural reductions in stroke volume (-47 +/- 3.7 and -48 +/- 3.3 ml, respectively) and increases in heart rate (35 +/- 6.6 and 51 +/- 5.2 beats/min, respectively). Cardiac output during standing was also similar (3.6 +/- 0.4 and 4.1 +/- 0.3 l/min, respectively). However, the finishers had a greater postflight vasoconstrictor response with higher total peripheral resistance during standing (22.3 +/- 1.2 units preflight and 29.4 +/- 2.3 units postflight) than did the nonfinishers (20.1 +/- 1.1 units preflight and 19.9 +/- 1.4 units postflight). We conclude that 1) the primary systemic hemodynamic event, i.e., the postural decrease in stroke volume, was similar in finishers and nonfinishers and 2) the heart rate response and cardiac output during standing were not significantly different, but 3) the postural vasoconstrictor response was significantly greater among the finishers (P < 0.01).

Central venous pressure in space

Gravity affects cardiac filling pressure and intravascular fluid distribution significantly. A major central fluid shift occurs when all hydrostatic gradients are abolished on entry into microgravity (microG). Understanding the dynamics of this shift requires continuous monitoring of cardiac filling pressure; central venous pressure (CVP) measurement is the only feasible means of accomplishing this. We directly measured CVP in three subjects: one aboard the Spacelab Life Sciences-1 space shuttle flight and two aboard the Spacelab Life Sciences-2 space shuttle flight. Continuous CVP measurements, with a 4-Fr catheter, began 4 h before launch and continued into microG. Mean CVP was 8.4 cmH2O seated before flight, 15.0 cmH2O in the supine legs-elevated posture in the shuttle, and 2.5 cmH2O after 10 min in microG. Although CVP decreased, the left ventricular end-diastolic dimension measured by echocardiography increased from a mean of 4.60 cm supine preflight to 4.97 cm within 48 h in microG. These data are consistent with increased cardiac filling early in microG despite a fall in CVP, suggesting that the relationship between CVP and actual transmural left ventricular filling pressure is altered in microG.

Mechanisms of post-flight orthostatic intolerance

Post-flight orthostatic intolerance is a dramatic physiological consequence of human adaptation to microgravity made inappropriate by a sudden return to 1-G. The immediate mechanism is almost always a failure to maintain adequate tissue perfusion, specifically perfusion of the central nervous system, but vestibular dysfunction may occasionally be the primary cause. Orthostatic intolerance is present in a wide range of clinical disorders of the nervous and cardiovascular systems. The intolerance that is produced by spaceflight and 1-G analogs (bed rest, head-down tilt at a moderate angle, water immersion) is different from its clinical counterparts by being only transiently present in subjects who otherwise have normal cardiovascular and regulatory systems. However, the same set of basic pathophysiological elements should be considered in the analysis of any form of orthostatic intolerance.

Central hemodynamics in a baboon model during microgravity induced by parabolic flight

We developed a chronically instrumented nonhuman primate model (baboon) to evaluate the central cardiovascular responses to transient microgravity induced by parabolic flight. Instrumentation provided simultaneous recording of high fidelity (Ao) and pulmonary artery (PA) pressures, right and left ventricular and atrial pressures, Ao and PA blood flow velocities and vessel dimensions, ECG and pleural pressures. Four daily flights in 1991 and five in 1992 were flown with forty parabola per flight. Animals flown in 1991 were not controlled for volume status. Animals flown in 1992 were studied in one of three conditions: 1) volume depleted by furosemide (DH), 2) volume expanded by saline infusion (VE), and 3) euvolemic (EU, no intervention, used for echo only). Mean right atrial pressures (RAP) during 1991 flights had a variable early microgravity response: increases in n=3 and decrease in n=3 (supine) and increases in n=5, decreases in n=2 (upright). In 1992 flights, DH, upright and supine, changed -10 +/- 4.1 mmHg, -3.2 +/- 2.2 mmHg, respectively (p < .05) compared to the pull-up phase. In contrast, VE changed (from pull-up to microgravity) +13 +/- 1.5 mmHg and +4.25 +/- 2.9 mmHg (upright and supine, respectively, p < .05). EU increased with microgravity +6.9 +/- .9 mmHg (upright only). LAP responses were similar, but more variable. Finally, heart chamber areas paralleled pressure changes. Thus, right and left heart filling pressure changes with sudden entry into microgravity conditions were dependent on initial circulatory volume status and somewhat modified by position (supine vs upright).

Effects of orthostatic and anti-orthostatic stress on patent and stenotic coronary arteries in swine

Head-up tilt (HUT) followed by head-down tilt (HDT) has been used to simulate the acute phase of adaptation to microgravity. This study evaluates the effects of HUT and HDT on the coronary circulation before and during coronary stenosis. Seven pigs were placed in the prone position and exposed to the following orientations for 20 min each: 1) 0 degrees horizontal (HZ); 2) +70 degrees HUT; and 3) -15 degrees HDT. The swine were then placed in the HZ position for 20 min while hemodynamics returned to baseline. The diameter of the left anterior descending (LAD) coronary artery was reduced to a point slightly less than that which produced a decrease in blood flow and the protocol was repeated. Heart rate (HR), contractility (dP/dt), mean arterial blood pressure (MABP), left ventricular pressure (LVP), coronary sinus pressure (CSP), left-ventricular end-diastolic pressure (LVEDP), coronary blood flow (CBF), coronary vascular resistance (CVR), myocardial oxygen consumption (MVO2) and coronary sinus lactate were determined after 20 min in each position. The transition from HUT to HDT elicited a significant (p < 0.05) increase in MABP, LVP, CSP, LVEDP, MVO2, and CBF and a significant decrease in CVR. During HDT, MVO2 increased 20 +/- 10% from Hz and 68 +/- 15% from HUT. There was a comparable increase in coronary artery flow. The hemodynamic responses were not significantly altered during pneumatic coronary occlusion. However, coronary sinus lactate was significantly elevated in the HDT positions. This study demonstrates a substantial increase in CBF during HUT to HDT with and without coronary stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular and metabolic responses to static contraction in man

There is substantial controversy regarding muscle blood flow and its regulation during static exercises. Major issues include (1) the relationship between developed force and muscle blood flow, (2) the ability of metabolic vasodilation to overcome neurally mediated vasoconstriction, (3) the time course and magnitude of hyperaemic flow following static exercise and (4) blood flow to the contralateral inactive limb. At rest, 15, 25 and 50% maximal voluntary contractions (MVC) femoral venous flow in four healthy young men (LBF; mean +/- 1 SD) was 0.4 +/- 0.3, 1.76 +/- 0.65, 0.90 +/- 0.32 and 1.06 +/- 0.59 1 min-1, and mean arterial pressures (MAP) were 104 +/- 13, 140 +/- 14, 160 +/- 17 and 161 +/- 11 mmHg. Thus, LBF does not increase proportionally with increasing levels of MVC, despite increased arterial pressure. Further, during both 25 and 50% MVC, which were held to exhaustion, an elevated limb vascular resistance was encountered towards the end of contraction, which suggests that neurally mediated vasoconstrictor activity overrides local vasodilation. Femoral venous effluent documented perfusion of active muscle during contractions of 15 and 25% MVC, but less so at 50% MVC. Immediately in recovery LBF reached levels of 3-3.5 1 min-1, which corresponded to 150 ml 100 g-1 min-1. When both O2 uptake and lactate release during the contractions and in recovery were taken into account, a close correlation between rate of energy turnover and exerted force was found. When MAP was raised by static contraction of the opposite quadriceps, LBF in the inactive leg increased momentarily. Within 1 min vascular resistance became elevated and the blood flow became reduced.

Hemodynamic, ventilatory, and biochemical responses of panic patients and normal controls with sodium lactate infusion and spontaneous panic attacks

Hemodynamic, ventilatory, and biochemical variables were measured in ten healthy adults and ten panic patients during infusion of 0.5 mol/L of sodium lactate. Physical activity, fitness level, and ambulatory electrocardiograms were also recorded. Lactate infusion doubled cardiac output, increased blood lactate levels by sixfold, and produced hypernatremia, hypocalcemia, and decreased serum bicarbonate levels in both groups but raised arterial pressure only in the patients. The patients hyperventilated before and during the infusion. Physiological responses and somatic complaints with the infusion differed little between the groups, but emotional complaints were six times more frequent among the panic patients. Eight patients but no control subjects interpreted their symptoms as a panic attack. Heart rate increased with only 14 of 31 recorded spontaneous outpatient panic attacks. Sodium lactate infusions appear to produce panic by mimicking the physiology of spontaneous panic. Treatment with cardioactive agents is not indicated in the absence of cardiopulmonary or autonomic nervous system abnormalities.

Cardiovascular effects of vasoactive intestinal peptide in healthy subjects

Hypotension and flushing are occasionally observed in patients with pancreatic cholera syndrome. Similar effects are produced when vasoactive intestinal polypeptide (VIP) is administered to healthy subjects. To characterize further these responses, serial measurements of heart rate, blood pressure, cardiac output and forearm blood flow were made in 6 healthy subjects during constant VIP infusion (400 pmol/kg/hr for 100 minutes). VIP infusion caused sustained vasodilatation and decreased total peripheral resistance and mean arterial pressure by 30 and 12%, respectively. Forearm resistance decreased by 65%. The effects on cardiac output and stroke volume were biphasic. During the early phase of VIP infusion (0 to 70 minutes), heart rate and cardiac output increased with only minor changes in stroke volume. Later (71 to 100 minutes) the tachycardia persisted, but cardiac output decreased toward control levels due to decreased stroke volume. Echocardiograms during the infusion demonstrated increased left ventricular contractility as defined by the relation between end-systolic wall stress and shortening fraction. These data document potent vasodilatory and inotropic actions of VIP. It is likely that intravascular volume losses from increased intestinal secretion account for the decreased stroke volume seen late in the VIP infusion period and immediately thereafter. The tachycardia appears to be an appropriate compensatory mechanism to maintain blood pressure in the presence of vasodilatation and loss of intervascular volume. These observations provide an explanation for the cardiovascular findings in patients with sudden release of VIP from tumors.

Echocardiographic measurements of left ventricular mass by a non-geometric method

The accuracy of a new non-geometric method for calculating left ventricular myocardial volumes from 2-D echocardiographic images was assessed in vitro using 20 formalin-fixed normal human hearts. Serial oblique short axis images were acquired from one point at 5 degree intervals, for a total of 10 to 12 cross sections. Echocardiographic myocardial volumes were calculated as the difference between the volumes defined by the epi- and endocardial surfaces. Actual myocardial volumes were determined by water displacement. Volumes ranged from 80 to 174 ml (mean 130.8 ml). Linear regression analysis demonstrated excellent agreement between echocardiographic (X) and direct measurements (Y) i.e., y = 0.98 X + 4.3 ml; r = 0.94; SEE = 8.4; p = 0.001. Comparison of 10 duplicate measurements by two independent observers yielded an r of 0.96. These in vitro results suggest that with this technique, quantitative analysis of a limited number of cross sectional echocardiographic views will provide accurate left ventricular mass estimates.

Right and left ventricular volumes in vitro by a new nongeometric method

We present an evaluation of a new nongeometric technique for calculating right and left ventricular volumes. This method calculates ventricular chamber volumes from multiple cross-sectional echocardiographic views taken from a single point as the echo beam is tilted progressively through the ventricle. Right and left ventricular volumes are calculated from both the approximate short axis and approximate apical position on 20 in vitro human hearts and compared with the actual chamber volumes. The results for both ventricles from both positions are excellent. Correlation coefficients are > 0.95 for all positions; the standard errors are in the range of 5 to 7 mL and the slopes and intercepts for the regression lines are not significantly different from 1 and 0, respectively (except for the left ventricular short-axis intercept). For all positions, approximately 6 to 8 views are needed for peak accuracy (7.5 degrees to 10 degrees separation). This approach offers several advantages. No geometric assumptions about ventricular shape are made. All images are acquired from a single point (or window), and the digitized points can be used to make a three-dimensional reconstruction of the ventricle. Also, during the calculations a volume distribution curve for the ventricle is produced. The shape of this curve can be characteristic for certain situations (ie, right ventricle, short axis) and can be used to make new simple equations for calculating volume. We conclude that this is an accurate nongeometric method for determining both right and left ventricular volumes in vitro.

Spacelab Life Sciences flight experiments: an integrated approach to the study of cardiovascular deconditioning and orthostatic hypotension

The microgravity environment of spaceflight produces rapid cardiovascular changes which are adaptive and appropriate in that setting, but are associated with significant deconditioning and orthostatic hypotension on return to Earth's gravity. The rapidity with which these space flight induced changes appear and disappear provides an ideal model for studying the underlying pathophysiological mechanisms of deconditioning and orthostatic hypotension, regardless of etiology. Since significant deconditioning is seen after flights of very short duration, muscle atrophy due to inactivity plays, at most, a small role. These changes in circulatory control associated with cephalad fluid shifts, rather than inactivity per se, are probably more important factors. In order to test this hypothesis in a systematic way, a multidisciplinary approach which defines and integrates inputs and responses from a wide variety of circulatory sub-systems is required. The cardiovascular experiments selected for Spacelab Life Sciences flights 1 and 2 provide such an approach. Both human and animal models will be utilized. Pre- and post-flight characterization of the payload crew includes determination of maximal exercise capacity (bicycle ergometry), orthostatic tolerance (lower body negative pressure), alpha and beta adrenergic sensitivity (isoproterenol and phenylephrine infusions), baroreflex sensitivity (ECG-gated, stepwise changes in carotid artery transmural pressure with a pneumatic neck collar), and responses to a 24 h period of 5 deg head-down tilt. Measurements of cardiac output (CO2 and C2H2 rebreathing), cardiac chamber dimensions (phased-array 2-dimensional echocardiography), direct central venous pressure, leg volume (Thornton sock), limb blood flow and venous compliance (occlusion plethysmography), blood and plasma volumes, renal plasma flow and glomerular filtration rates, and various hormonal levels including catecholamines and atrial natriuretic factor will also be obtained. The central venous catheter will be inserted immediately pre-launch and monitored with heart rate and blood pressure in-flight until cardiac output, respiratory gas exchange and quantitative 2D echocardiography measurements can be performed. In-flight hemodynamic measurements will be repeated at rest and during submaximal exercise daily and also during maximal exercise midway through the flight to document the timecourse and extent of cardiovascular changes in the payload crew. Parallel studies are planned for the animals. In addition to measurements of right atrial and aortic pressures and cardiac output, a dorsal micro-circulatory chamber will allow determinations of changes in capillary and venular architecture and function in six of the rats. The techniques and findings from many of the SLS-1 and 2 supporting studies have already yielded significant information about circulatory regulation in patients with both hypo- and hypertension. The flight experiments themselves will provide new data to test the validity of both animal and human models currently used for simulating the fluid shifts of a micro-gravity environment. The development of effective countermeasures, not only for short and long duration space travellers, but also for Earth-bound medical patients can then be physiologically based on experimental data rather than anecdote.

Comparative efficacy of behavioral stress management versus propranolol in reducing psychophysiological reactivity in post-myocardial infarction patients

The present study compared the relative efficacy of a behavioral stress-management procedure versus a pharmacologic method (the beta-blocker propranolol) in reducing psychophysiological reactivity in post-myocardial infarction (MI) patients. A pretreatment-posttreatment assessment design was used, with 10 patients participating in six separate sessions. The first session involved evaluating psychophysiological reactivity to an emotional stressor (a public-speaking task). The subsequent five sessions involved the administration of the respective treatments, either stress management or drug. The patients were randomly assigned to each treatment group. The public-speaking stressor was readministered after the last treatment session. Results demonstrated that behavioral stress management reduced psychophysiological reactivity to public speaking to the same level seen with propranolol. The findings suggest that this nonpharmacological approach could be of use when beta-blocker therapy is not desired, not practical, or medically contraindicated.

Cardiovascular deconditioning produced by 20 hours of bedrest with head-down tilt (-5 degrees) in middle-aged healthy men

Cardiovascular deconditioning after prolonged bedrest has been attributed to inactivity. To examine the role of the altered distribution of body fluids, 5 healthy men, aged 41 to 48 years, were studied before, during and after a 20-hour period of bedrest with head-down tilt (-5 degrees). This intervention produces a marked central shift of intravascular and interstitial fluid, but the short duration minimizes the effects of inactivity. Central venous pressure, cardiac output and stroke volume all increased significantly (p less than 0.05) from supine baseline mean values; central venous pressure from 8.6 to 12.6 cm H2O, cardiac output from 6.9 to 7.9 liters/min, and stroke volume from 104 to 113 ml after 15 minutes of tilt, but all values returned to baseline within 20 hours. Supine central venous pressure after tilt was 7.4 cm H2O, cardiac output 5.7 liters/min and stroke volume 84 ml. Blood volume decreased 0.51 liters. After tilt, orthostatic stress produced a higher heart rate (90 +/- 18 vs 68 +/- 12 beats/min). Maximal oxygen consumption decreased (2.36 +/- 0.41 vs 2.62 +/- 0.48 liters/min), mainly owing to reduced stroke volume (87 +/- 22 vs 107 +/- 18 ml, p less than 0.05). Thus, tilt produced a transient increase in central venous pressure, stroke volume and cardiac output, but supine mean values were below baseline levels after 20 hours. The post-tilt state was qualitatively and quantitatively similar to that seen after 2 to 3 weeks of bedrest or several days of spaceflight. These results are also similar to those from a previously studied group of ten 20- to 30-year-old normal men.(ABSTRACT TRUNCATED AT 250 WORDS)

Single and combined therapy for systemic hypertension with propranolol, hydralazine and hydrochlorothiazide: hemodynamic and neuroendocrine mechanisms of action

The antihypertensive mechanisms of single and combined therapy with a beta-adrenergic antagonist (propranolol) and a vasodilator (hydralazine) were investigated in 9 patients with moderately severe hypertension, who were receiving maintenance diuretic (hydrochlorothiazide) treatment. Hemodynamic and neuroendocrine responses were determined at rest and during lower body negative pressure, and dynamic and static exercise stress after the chronic administration of propranolol and hydralazine, given alone or in combination. All 3 drug regimens, each administered for at least 10 weeks, reduced blood pressure (p less than 0.05) compared with diuretic-only therapy in patients at rest, in both the supine and standing position, and during lower body negative pressure and dynamic exercise. There was a significant additive antihypertensive effect when propranolol and hydralazine were combined. Only combination therapy effectively lowered pressure during static exercise. The regimens produced divergent effects on the supine cardiac output: a decrease with propranolol (p less than 0.05), no change with combination therapy and an increase with hydralazine (p less than 0.05). Both hydralazine and combination therapy significantly reduced supine total peripheral resistance (p less than 0.05), whereas propranolol produced no change. All 3 drug treatments significantly reduced total peripheral resistance during upright rest and dynamic exercise (p less than 0.05), without changing cardiac output or maximal exercise capacity. During exercise, cardiac output was maintained in patients treated with propranolol and in those treated with combined therapy by increases in stroke volume (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Body size, composition, and fitness in adolescents with elevated blood pressures

Increased body size is often found in children with elevated blood pressures, but it is not clear whether this is a result of obesity or early maturity. Similarly, levels of activity and fitness have marked effects on blood pressure and body composition. To study these interrelated factors, we measured height, weight, and body composition (skinfold thickness and total body water) as well as heart rate, blood pressure, and oxygen consumption at rest and during exercise in 192 ninth grade boys and girls, 102 with persistently elevated blood pressures at or above the 95th percentile and 90 matched controls with blood pressures below the 50th percentile for the entire population of 10,641 Dallas County ninth graders tested. Differences in resting blood pressures also were present during maximal exercise and recovery periods. Boys with persistently elevated blood pressures were characterized by increased supine and recovery heart rates, normal fitness, excess size for age in the absence of obesity, and early maturation. Girls with persistently elevated blood pressures had increased heart rates, decreased fitness, and obesity.

Oxygen uptake and cardiovascular responses in control adults and acute myocardial infarction patients during bathing

Physiological responses before, during, and after three types of baths were determined in 18 patients who were 5 to 17 days postinfarction and 22 control adults. In the patients, oxygen consumption (VO2) averaged 6, 7, and 7 ml/kg/min, peak heart rate 105, 108, and 112 beats per minute, and rate pressure product 115, 120, and 111 for basin, tub, and shower bathing, respectively. Oxygen consumption during bathing was less than 3 times resting levels. The patients had a significantly lower VO2 during bathing than the control subjects. The patients' peak heart rates were higher than anticipated for the level of exertion, and sometimes exceeded the target heart rates used in predischarge testing. Peak heart rate and occurrence of dysrhythmia did not differ significantly between the three types of baths. In the women patients, rate pressure product was significantly higher after tub bath than after basin bath or shower. The subjects had no cardiovascular symptoms during bathing, rated all three baths as light exertion, and disliked the basin bath. The data show that the physiologic costs of the three types of baths are similar, differences in responses to bathing seem more a function of subject variability than bath type, and many cardiac patients can take a tub bath or shower earlier in their hospitalization. However, more research is needed to predict patients likely to have an exaggerated response to bathing and to develop clear guidelines for bath method selection and progression.

Body size, composition, and fitness in adolescents with elevated blood pressures

Increased body size is often found in children with elevated blood pressures, but it is not clear whether this is a result of obesity or early maturity. Similarly, levels of activity and fitness have marked effects on blood pressure and body composition. To study these interrelated factors, we measured height, weight, and body composition (skinfold thickness and total body water) as well as heart rate, blood pressure, and oxygen consumption at rest and during exercise in 192 ninth grade boys and girls, 102 with persistently elevated blood pressures at or above the 95th percentile and 90 matched controls with blood pressures below the 50th percentile for the entire population of 10,641 Dallas County ninth graders tested. Differences in resting blood pressures also were present during maximal exercise and recovery periods. Boys with persistently elevated blood pressures were characterized by increased supine and recovery heart rates, normal fitness, excess size for age in the absence of obesity, and early maturation. Girls with persistently elevated blood pressures had increased heart rates, decreased fitness, and obesity.