Physiology and Respiratory Changes in Space Travel PDF

Physiologic and Respiratory Changes in Space Travel (Understanding Human Adaptations to Microgravity) Presentation by Ajayi Lukman 1 Outlines Introduction Objectives Physiologic changes The musculoskeletal system The cardiovascular system Sho...

Physiologic and Respiratory Changes in Space Travel (Understanding Human Adaptations to Microgravity) Presentation by Ajayi Lukman 1 Outlines Introduction Objectives Physiologic changes The musculoskeletal system The cardiovascular system Short-term and Long-term implications Respiratory system Distribution of pulmonary blood flow Effects of microgravity and gravity on the lungs References 2 Introduction Sending humans to explore the moon has opened avenues for understanding the impacts of exposure to altered gravity environments. It has allowed researchers to examine the effects on different physiological systems (Nandu et al., 2021). Outer space presents several unique environmental conditions, including microgravity, radiation, hypoxia, and fluid shifts (Satoshi et al., 2020). During space flights, astronauts experience three stages of physiological adaptation related to gravity: (1) changes upon entering microgravity, (2) changes that occur after prolonged exposure to microgravity, and (3) readaptation to 1G gravity on Earth after returning from space (Satoshi et al., 2020). 3 Introduction (cont’d) Microgravity affects several physiological systems, including the neuro-vestibular, cardiovascular, musculoskeletal, respiratory, and immuno- hematological systems. 4 Objectives To understand the physiological effect of microgravity on human health To Analyze and understand the physiological changes associated with some of these systems during the adaptation phase. To examine the respiratory adaptations in microgravity. 5 Physiological changes Musculoskeletal system (impact on muscles and bones) Cardiovascular system (heart and fluid shifts) 6 The musculoskeletal system The effects of the space environment on bone health has been of scientific concern. During exposure to microgravity, bone resorption increases significantly, while bone formation remains unchanged or decreases (Stavroula et al., 2022). This imbalance leads to 1–1.5% bone mass loss per month (Stavnichuk et al., 2020). 7 The musculoskeletal system (cont’d) Spaceflight-induced bone loss varies between skeletal sites. For example, bone tissue is better preserved in the non- weight-bearing upper limbs than the weight-bearing lower limbs(Stavroula et al., 2022). The increased level of bone resorption is associated with increased levels of calcium and other minerals in the blood circulation and the increased excretion of it in the urine(Liakopoulos et al., 2012; Gabel et al., 2022) This process enhances the astronauts’ risk of developing kidney stones during and after the spaceflight(Liakopoulos et al., 2012; Gabel et al., 2022) 8 Sourced from: Chaloulakou, S., Poulia, K. A., & Karayiannis, D. (2022). Physiological alterations in relation to space flight: the role of nutrition. Nutrients, 14(22), 4896. 9 The musculoskeletal system (cont’d) Astronauts experience incomplete recovery from bone loss in their tibia even one year after returning from spaceflight(Gabel et al., 2022). The flight duration is directly proportional to the extent of bone loss: the longer the spaceflight, the greater the loss and the more challenging the recovery process (Gabel et al., 2022). In addition to bone loss, astronauts experience muscle loss and rapid atrophy of skeletal muscle. In microgravity conditions, movements demand minimal muscle effort and force, leading to a decrease in muscle mass and volume, particularly in the lower limbs (Comfort et al., 2021; Lang et al., 2004). 10 The musculoskeletal system (cont’d) This decrease in muscle mass leads to weakness and diminished functional capacity, which is particularly noticeable in astronauts upon their return to a gravity condition(Vico et al., 2017). 11 The Cardiovascular System Influences of spaceflight on the cardiovascular system begin even before liftoff with preparatory measures, such as the preflight posture. Several hours before takeoff, astronauts take their positions in the shuttle, lying on their backs with a 90⁰ hip and knee flexion. 12 The Cardiovascular System (cont’d) This supine position prevents blood from pooling in the legs during ascent which in extreme cases, could lead to syncope (passing out). It also means that a significant blood volume will be placed above the heart and fluid will begin to move from the periphery to the upper body, indicating what will continue to happen in space. 13 Hanns-Christian Gunga, Weller, V., Hans-Joachim Appell Coriolano, Werner, A., & Uwe Hoffmann. (2016). Cardiovascular System, Red Blood Cells, and Oxygen Transport in Microgravity. Cham Springer International Publishing. 14 The Cardiovascular System (cont’d) Body fluid redistribution occurs due to microgravity which leads to approximately 2 L of fluid shifting to the upper limbs and head, thus increasing the preload and stroke volume which in turn increases cardiac output (CO) by 18– 26%( Baran et al., 2021; Sandal et al., 2020). fluid shift also causes a decrease in the circulating blood volume (10–15%), aerobic capacity, and heart size (cardiac atrophy) (Petal et al., 2020; Moore et al., 2014). These changes are associated with orthostatic hypotension, a phenomenon that most astronauts experience after a spaceflight (Baran et al., 2021; Mulavra et al., 2018) 15 Short -Term and Long-Term Cardiovascular Adaptation There are several short-term cardiovascular adaptations to the fluid shift. The cardiovascular system initiates a range of primary responses to adapt to the increased thoracic volume in the short term. This rapid reaction involves a decrease in the heart rate, as well as a dilatation of arterioles to decrease peripheral resistance and thereby decrease blood pressure (Fritsch-Yelle et al., 1996). 16 Short -Term and Long-Term Cardiovascular Adaptation Subsequently, there are long-term adaptations to fluid shifts that result in decreased fluid volume. The body perceives a fluid overload due to a high thoracic filling which leads to a reduction in blood volume via; i. Reduction in thirst which leads to a decrease in fluid intake ii. Fluid movement from the intravascular compartment into the interstitial space (Hanns-Christian et al., 2016). 17 The Respiratory System The lung is a network of airways, alveoli, and blood vessels, which in Earth’s gravity, deforms under its weight, so the structure of the lung is more condensed at the bottom than at the top (Prisk 2019). This results in greater ventilation and perfusion at the bottom or dependent region of the lung compared to the top, where the alveoli are greatly expanded and there is very little perfusion. This heterogeneity results in heterogeneity in the ventilation-perfusion ratio throughout the lungs. 18 The Distribution of pulmonary blood flow When a person is supine, blood flow is nearly uniform throughout the lung. When a person is standing, blood flow is unevenly distributed because of the effect of gravity. Blood flow is lowest at the apex of the lung (zone 1) and highest at the base of the lung (zone 3). Zone 1—blood flow is lowest. Alveolar pressure > arterial pressure > venous pressure. 19 Distribution of Pulmonary Blood Flow The high alveolar pressure may compress the capillaries and reduce blood flow in zone 1. Zone 1 likely does not exist in a healthy individual's lungs as pulmonary arterial pressures just exceed that of alveolar pressure even at the top of the lung apex. This situation can occur if arterial blood pressure is decreased as a result of hemorrhage or if alveolar pressure is increased because of positive pressure ventilation. 2. Zone 2—blood flow is medium. Arterial pressure > alveolar pressure > venous pressure. 20 Distribution of Pulmonary Blood Flow Moving down the lung, arterial pressure progressively increases because of gravitational effects on arterial pressure. Arterial pressure is greater than alveolar pressure in zone 2, and blood flow is driven by the difference between arterial pressure and alveolar pressure. Zone 3—blood flow is highest. Arterial pressure > venous pressure > alveolar pressure. Moving down toward the base of the lung, arterial pressure is highest because of gravitational effects and venous pressure finally increases to the point 21 22 Effects of microgravity and gravity on the lungs it is known that the removal of gravity dependence for blood flow allows for homogenous lung perfusion (Ardejani and Saleem., 2022) This reduction in heterogeneity would lead one to assume that the heterogeneity of the ventilation- perfusion ratio would also be reduced. However, surprisingly, this is not the case, some heterogeneity remains in microgravity 23  Gravity and microgravity have similar effects on ventilation and perfusion, ensuring that their matching and the efficiency of gas exchange are maintained during spaceflight.(Prisk 2014) Therefore, the removal of gravity causes an upward shift of blood and fluids into the thorax, which has various effects on the respiratory system. 24 Effects of microgravity and gravity on the lungs The upward shift causes an increase in pulmonary blood volume. As the lungs receive approximately 100% of the cardiac output (CO), the initial increase in CO of astronauts increases pulmonary blood flow (Prisk 2018; West et al., 1997) The removal of gravity enables more uniform expansion of the alveoli, which increases the surface area exposed to the external environment. As a result, there is a reduction in alveolar dead space and improved ventilation in the upper regions of the lung compared to conditions with normal gravity (Prisk 2014). 25 Effects of microgravity and gravity on the lungs This increase in ventilation, in addition to the 28% increase in pulmonary blood volume, causes an increase in the diffusing capacity of the alveoli by approximately 28% (Prisk 2019; West et al., 1997). This increase remains elevated during the entire duration of microgravity exposure (Prisk 2019). 26 Countermeasures Breathing devices such as Respiratory muscle training (RMT) device to strengthen respiratory muscles and improve breathing efficiency Regular physical activities – Aerobic exercise (e.g. treadmill running, cycling) to increase respiratory rate and airflow. Preflight lung function testing and training – astronauts undergo spirometry tests before missions to asses lung function and practice breathing techniques. 27 Conclusions Spaceflight stressors have been associated with pathological changes in astronauts’ physiology. Several deconditioning states in the cardiovascular, respiratory, musculoskeletal, bone metabolic, hematological and immunological, and central nervous systems have been documented, and efforts to ameliorate the symptoms have been made. 28 References Gabel, L.; Liphardt, A.-M.; Hulme, A.P.; Heer, M.; Zwart, S.R.; Sibonga, J.D.; Smith, S.M.; Boyd, S.K. Pre-flight exercise and bone metabolism predict unloading-induced bone loss due to spaceflight. Br. J. Sports Med. 2022, 56, 196–203 Hanns-Christian Gunga, Weller, V., Hans-Joachim Appell Coriolano, Werner, A., & Uwe Hoffmann. (2016). Cardiovascular System, Red Blood Cells, and Oxygen Transport in Microgravity. Cham Springer International Publishing. Lang, T.; Leblanc, A.; Evans, H.; Lu, Y.; Genant, H.; Yu, A. Cortical and Trabecular Bone Mineral Loss from the Spine and Hip in Long- Duration Spaceflight. J. Bone Miner. Res. 2004, 19, 1006–1012. [CrossRef] [PubMed] 29 References Moore AD, Downs ME, Lee SMC, Feiveson AH, Knudsen P, Ploutz- Snyder L (2014) Peak exercise oxygen uptake during and following long-duration spaceflight. J Appl Physiol 117:231–238 Prisk GK, Fine JM, Cooper TK, West JB (2006) Vital capacity, respiratory muscle strength and pulmonary gas exchange during long-duration exposure to microgravity. J Appl Physiol 101:439– 447 Prisk GK (2014) Microgravity and the respiratory system. Eur Respir J 43:1459–1471 Stavnichuk, M.; Mikolajewicz, N.; Corlett, T.; Morris, M.; Komarova, S.V. A systematic review and meta-analysis of bone loss in space travelers. npj Microgravity 2020, 6, 13. [CrossRef] 30