Cardiovascular Responses to Commonly Used Tests In and Outside of the Laboratory Settings

Several tests are available for assessing cardiovascular response to various interventions which may be given in the laboratory, or outside of it in the field. The tests are meant to excite or deactivate cardiovascular and other sensory receptors which signal the central mechanisms. They have been found useful in generating data to study cardiovascular effects on subjects exposed to specialized physical training (e.g., athletes), in the evaluation of people engaged in special occupations such as pilots, astronauts, and other military personnel, and in training undergraduate and postgraduate students. If the response does not fit into the physiological norm, it may reflect a temporary aberration, or a more serious defect in the cardiovascular control mechanism because of disease. Interpretation of data generated may vary between various operators/observers. Here, an attempt has been made to bring out responses of the cardiovascular system to the commonly used tests, and their applicability in clinical situations.

Introduction to cuban space physiology meeting and gravity of exercise for a mission to Mars

In order to develop effective countermeasures to maintain the health and well-being of crew members during prolonged spaceflight, such as a mission to Mars, an integrated physiologic view is necessary. Future spacecraft to deep space will be constrained by limited volume, food, water, shelter and other resources. Thus, it's important to understand the highest risks and to direct research into these areas. This review paper examines important risks during a 2-3 year mission to Mars with a view to provide devices and methods to integrate across many physiologic systems in an attempt to reproduce activities of daily living on Earth. Because effective hardware for artificial gravity by centrifugation may be decades away, we propose use of lower body negative pressure (LBNP) as means to simulate multiple beneficial effects of gravitational stress including blood and fluid shifts towards the feet and mechanical loading of the body. LBNP-devices are reconfigurable as wearable suits to reduce mass or combined with exercise devices to increase efficacy of exercise in weightlessness.

Para desarrollar contramedidas efectivas para mantener la salud y el bienestar de los miembros de la tripulación durante un vuelo espacial prolongado, como una misión a Marte, es necesaria una visión fisiológica integrada. Las naves espaciales futuras al espacio profundo estarán limitadas por un volumen limitado, alimentos, agua, refugio y otros recursos. Por lo tanto, es importante comprender los riesgos más altos y dirigir la investigación en estas áreas. Este documento de revisión examina riesgos importantes durante una misión de 2-3 años a Marte con el fin de proporcionar dispositivos y métodos para integrarse en muchos sistemas fisiológicos en un intento de reproducir las actividades de la vida diaria en la Tierra. Debido a que el hardware efectivo para la gravedad artificial por centrifugación puede estar a décadas de distancia, proponemos el uso de la presión negativa de la parte inferior del cuerpo (LBNP) como un medio para simular múltiples efectos beneficiosos del estrés gravitacional, incluidos los cambios de sangre y fluidos hacia los pies y la carga mecánica del cuerpo. Los dispositivos LBNP son reconfigurables como trajes portátiles para reducir la masa o combinados con dispositivos de ejercicio para aumentar la eficacia del ejercicio en la ingravidez.

Nitroglycerin reduces augmentation index and central blood pressure independent of effects on cardiac preload / 药物分析学报

Objective To determine whether reduction In central pressure augmentation and central systolic blood pressure by nitroglycerine (NTG) results from effects on pre-lead or is due to arterial dilation. Methods We compared effects of NTG with these of lower body negative pressure (LBNP). Hemodyunmic measurements were made at rest, during LBNP (10, 20 and 30 mmHg, each for 15 min) and after NTG (10, 30 and 100μg/min, each dose for 15 min) in ten healthy volunteers. Cardiac pre-lead, stroke volume and cardiac output were assessed by echacardiography. Central pressure an mnentation and central systolic pressure were obtained by radial tonometry using a transfer function. Results LBNP (20 mmHg) and NTG (30μg/min) reduced pre-lead (as measured by the peak velocity of the S wave in the superior vena eava) to a similar degree [by (26. 8 ± 3.8) % and (23.9 ± 3. 4) %, respectively]. Compared to LBNP, NTG reduced systemic vascular resistance [by (32. 9 ± 7.5) %, p< 0. 01], decreased peripheral and central pressure augmentation [by (20. 8 ± 3. 4)% units and (12. 9±2. 9)% units, respectively, each P< 0. 01]. Conclusion These results suggest that a reduction in pre-load does not explain reduction in pressure augmentation and central systolic blood pressure by NTG and that these effects are mediated through arterial dilation.

Measurement of respiratory pulse transit time variation as an intravascular volume index in simulated hemorrhage / 대한마취과학회지

BACKGROUND: We examined the usefulness of respiratory pulse transit time (PTT) variation as an intravascular volume index in young, healthy, spontaneous, paced breathing volunteers exposed to simulated central hypovolemia by lower body negative pressure (LBNP). METHODS: With paced breathing at 0.25 Hz, beat-to-beat finger blood pressure (BP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral resistance (TPR), and PTT were measured non-invasively in 18 healthy volunteers. Graded central hypovolemia was generated using LBNP from 0 to -20, -30, -40, and -50 mmHg. Respiratory PTT variation (PTTV) was calculated as the difference of maximal and minimal values divided by their respective means. Respiratory-frequency PTT variability (PTTRF) using power spectral analysis was also estimated. RESULTS: During LBNP, SV, CO and PTTRF decreased, but PTT, PTTV and TPR increased significantly. PTTV did not correlate with SV changes (r = -0.08, P = 0.52), but PTTRF (r = 0.58, P < 0.01) and PTT (r = 0.43, P < 0.01) did during progressive hypovolemia. CONCLUSIONS: PTTRF is more applicable to the changes in intravascular volume than PTT and PTTV, suggesting spectral analysis of PTT might be used as a dynamic preload index in patients with spontaneous and paced breathing condition, which needs further studies.

Nitroglycerin reduces augmentation index and central blood pressure independent of effects on cardiac preload / 西安交通大学学报·英文版

Objective: To determine whether reduction in central pressure augmentation and central systolic blood pressure by nitroglycerine (NTG) results from effects on pre-load or is due to arterial dilation. Methods: We compared effects of NTG with those of lower body negative pressure (LBNP). Hemodynamic measurements were made at rest, during LBNP (10, 20 and 30 mmHg, each for 15 min) and after NTG (10, 30 and 100 μg/min, each dose for 15 min) in ten healthy volunteers. Cardiac pre-load, stroke volume and cardiac output were assessed by echocardiography. Central pressure augmentation and central systolic pressure were obtained by radial tonometry using a transfer function. Results: LBNP (20 mmHg) and NTG (30 μg/min) reduced pre-load (as measured by the peak velocity of the S wave in the superior vena cava) to a similar degree [by (26.8 ± 3.8)% and (23.9 ± 3.4)%, respectively]. Compared to LBNP, NTG reduced systemic vascular resistance [by (32.9± 7.5)%, P<0.01], decreased peripheral and central pressure augmentation [by (20.8 ± 3.4)% units and (12.9 ± 2.9)% units, respectively, each P<0.01]. Conclusion: These results suggest that a reduction in pre-load does not explain reduction in pressure augmentation and central systolic blood pressure by NTG and that these effects are mediated through arterial dilation.

Changes of Tolerance and Cardiovascular Responses to Head-up Tilte Combined with LBNP Following Preceding Exposure to Head-down Tilt / 航天医学与医学工程

Objective To observe pre-syncopal limited tolerance and cardiovascular responses to head-up tilt combined with lower body negative pressure (HUT/LBNP) following exposure to head-down tilt (HDT, -1 Gz). Method Exposures to HUT/LBNP (-60 mmHg) in control session (without preceding 30 s -1 Gz treatment) and in simulated push-pull effect (PPE) session (with preceding 30 s -1 Gz treatment) were performed in 8 healthy adults. The changes of hemodynamic parameters were monitored by electrical impedance instrument during the experiments. Result The mean endurance time in presyncopal symptom limited HUT/LBNP in control session and in simulated PPE session were 8.4±2.1 min and 4.5±2.4 min, respectively, the two means were significantly different (P< 0.01). In simulated PPE session, as compared with baseline, heart rate (HR) during HDT was significantly lowered (P<0.01), while stroke volume (SV) and cardiac output (CO) were increased significantly (P<0.01). During HUT/LBNP, the increased percentage (relative to baseline) of HR in PPE session was lower than these in control session (P<0.05); the decreased percentages of SV and CO during HUT/LBNP in PPE session were both higher than those in control session (P<0.05). During HUT/LBNP, arterial pulse pressure (PP) of control session was significantly decreased than the value of baseline value (P<0.05); Total peripheral resistance (TPR) of PPE session was significantly increased than baseline value (P<0.05). Conclusion Tolerance time before the appearance of presyncopal symptoms during HUT/LBNP decreases and cardiovascular responses to HUT/LBNP are impaired, preceding exposure to HDT.

EFFECT OF LBNP ON REGULATIVE MECHANISMS OF CARDIOVASCULAR SYSTEM OF MALE AND FEMALE PILOT-STUDENTS / 解放军医学杂志

To analyze the change of physiological indices in male and female pilot students during lower body negative pressure (LBNP) exposure, one female group and one male group participated in the experiment. They were subjected to LBNP up to 50 mmHg for 8 min. Electrocardiogram (ECG), heart rate (HR), blood pressure (BP), cerebral blood flow (CBF) and time of exposure were monitored during LBNP. The results showed that during LBNP, heart rate (HR) increased while systolic blood pressure (SBP) and cerebral blood flow (CBF) decreased with the prolongation of exposure. It is concluded that LBNP exposure could produce similar physiological changes in both male and femal pilot students.

The diagnosis and treatment of abdominal compartment syndrome: report of five patients / 中国普通外科杂志

Objective To sum up the experience on the diagnosis and treatment of abdominal compartment syndrome(ACS). Methods In this report, ACS was diagnosed by special clinical features in all 5 patients. Following emergency decompressive celiotomy, the abdominal viscera were covered with a 3 L sterile plastic bag for nutrition support. Results The first case died despite abdominal decompression through uper midline incision. 4 cases underwent decompressive celiotomy through incision from xiphoid to symphysis, one died postoperatively. The overall mortality in this series was 40% (2 / 5). Conclusions Close attention paid to the abdominal and systemic signs facilitates the diagnosis of ACS.Emergent decompressive celiotomy through a incision from xiphoid to symphysis is effective in treating ACS. Temporary abdominal closure could be fulfiled with 3L sterile plastic bag for nutrition support.