**4.2 Endothelial changes**

Microgravity and reduced motor activity produces endothelial changes by altering the regional blood flow and vascular transmural pressure, which in turn, produces an adaptation of vasomotor tone and long term vascular remodelling mainly in the endothelium and smooth muscular cells [16].

This microvascular endothelial dysfunction in astronauts, plays a material role in osteoporosis, muscle atrophy and cardiovascular deconditioning considering that the endothelial cells of the microvasculature cover a surface area that is fifty times larger than that of all the large vessels put together [15].

#### **4.3 Space motion sickness**

Space motion sickness is a result of neurovestibular disturbance that happens to about two-thirds of astronauts. It occurs within a few minutes of being in space and gradually resolves over a period of 48–72 hours. Nevertheless, it can last up to a few days and can reappear after landing. Some causes that are suggested as a possible hypothesis include: an increase in cerebrospinal fluid and intracranial pressure due to the headward fluid shift, a lowered threshold for vestibular stimulation due to central volume expansion and the absence of gravity triggering an abnormal vestibular activity leading to a parasympathetic overstimulation [15, 23].

Space motion sickness is characterised by an imbalance in spatial orientation, balance, gaze control and autonomous vestibular function. Symptoms include facial pallor, cold sweating, stomach awareness, anorexia, vomiting, nausea, headache and malaise [2, 15, 16].

#### **4.4 Eye**

On Earth, venous return from the head, neck and upper trunk is supported by gravity. Unlike the lower half of the body, the veins draining this region do not have valves and lack muscular contraction. In space, there is reduced arterial blood supply and venous flow from the eye. This increases the venous pressure and filtration at the capillaries causing an increase in both intracranial pressure and IOP [15].

#### **4.5 Effects on the musculoskeletal system**

Extended exposure to microgravity leads to a loss of bone and muscle mass due to its reduced use and perfusion changes. Inadequate nutrition and stress are additional reasons that lead to muscle atrophy [2]. Weight bearing bones: lumbar spine, pelvis, femoral neck and trochanter, and calcaneus and postural muscles: back, abdominal wall, lower limbs are most commonly affected [2, 24].

In addition to absence of gravitational loading, decreased Vitamin D production—partly due to low levels of sunlight—leads to decreased calcium fixation in bones and reabsorption in kidneys. Higher ambient levels of carbon dioxide, leading to respiratory acidosis also contribute to bone loss [2, 15] Increase in urinary calcium coupled with a reduction in diuresis and decreased fluid intake increases the risk of kidney stones [25–27].

#### **4.6 Effects on the respiratory system**

Microgravity induced changes in the lungs have been the subject of much interest for decades. The ventilation to perfusion ratio attains equilibrium in the absence of gravity [15, 16]. There is an increase in the total alveolocapillary surface which in turn improves the lung diffusing capacity [16]. Gas exchange in space does not undergo a substantial change but there is reduced oxygen consumption and carbon dioxide production. This is attributed to a reduced physical activity in space

**199**

*Challenges to Airway Management in Space DOI: http://dx.doi.org/10.5772/intechopen.98932*

at FRC however is not affected [15].

**4.7 Immune system**

centres [2].

even malignancies [3].

**4.8 Gastrointestinal motility**

intake and caloric expenditure [16, 33, 34].

fined habitats [3].

**4.9 Weight loss**

function [16].

and change in the ventilation to perfusion ratios between the upper and lower lung regions. These factors lead to an overall reduction in the metabolic rate [15].

Microgravity can cause weakening of the respiratory muscles leading to a reduced rib cage expansion. Thus, there is an increased contribution of the abdomen to tidal volume [28]. Intra-abdominal pathology and subsequent intraabdominal hypertension is important to providing life support and mechanical ventilation. However, it has been demonstrated that intra-abdominal gas insufflation during laparoscopic surgery in space and the subsequent intra-abdominal

hypertension is made better by the absence of gravity [15, 16].

Changes in the thoracoabdominal compliance is advantageous to the pulmonary

It has been suggested that changes in the respiratory system are similar to those that occur to individuals on prolonged bed rest and are anatomical in nature [15]. These typically occur over several weeks. There is a significant reduction in tidal volume [15, 16] and residual volume [29]. Vital capacity and forced vital capacity reduce initially followed by subsequent recovery. Functional residual capacity (FRC) reduces by 500 ml and remains at that level for the remainder of the period in space [29, 30]. Peak inspiratory and expiratory flows are also not significantly altered. However maximum inspiratory pressure significantly reduces, while the maximum expiratory pressure (MEP) at total lung volume initially reduces at month 2 and month 4, but recovers by month 6 of being in microgravity. The MEP

Immune system dysregulation occurs in space. High levels of physical and psychological stress—immediately before and after space flight— physiological stress, isolation, confinement, disrupted circadian rhythms are some of the contributing factors to immune system dysregulation [2]. Additionally, increase in levels of glucocorticoids and catecholamines, may also contribute to change in the immune system [3, 31]. Various studies have demonstrated that lack of gravity impairs the signalling pathways that are necessary for early T-cell activation. This leads to changes in the organisation of the cytoskeleton and microtubule organising

Immune system dysregulation can lead to an increased incidence of hypersensitivities, autoimmunity, allergies, infectious diseases, latent viral reactivation and

Microbes undergo several changes in their characteristics in space. Notably, bacteria cultured on board have increased pathogenicity [32]. The microorganisms present in the human body, are transmitted easily between persons, in such con-

Gastrointestinal motility is reduced in space especially in the first 72 hours. It has

Astronauts experience a weight loss of up to 5% after a 6 month stay on the International Space Station (ISS). This is explained by a mismatch between caloric

also been observed that the gastric content pH decreases [16].

#### *Challenges to Airway Management in Space DOI: http://dx.doi.org/10.5772/intechopen.98932*

*Special Considerations in Human Airway Management*

**4.3 Space motion sickness**

and malaise [2, 15, 16].

**4.5 Effects on the musculoskeletal system**

the risk of kidney stones [25–27].

**4.6 Effects on the respiratory system**

**4.4 Eye**

mainly in the endothelium and smooth muscular cells [16].

larger than that of all the large vessels put together [15].

produces an adaptation of vasomotor tone and long term vascular remodelling

This microvascular endothelial dysfunction in astronauts, plays a material role in osteoporosis, muscle atrophy and cardiovascular deconditioning considering that the endothelial cells of the microvasculature cover a surface area that is fifty times

Space motion sickness is a result of neurovestibular disturbance that happens to about two-thirds of astronauts. It occurs within a few minutes of being in space and gradually resolves over a period of 48–72 hours. Nevertheless, it can last up to a few days and can reappear after landing. Some causes that are suggested as a possible hypothesis include: an increase in cerebrospinal fluid and intracranial pressure due to the headward fluid shift, a lowered threshold for vestibular stimulation due to central volume expansion and the absence of gravity triggering an abnormal vestibular activity leading to a parasympathetic overstimulation [15, 23].

Space motion sickness is characterised by an imbalance in spatial orientation, balance, gaze control and autonomous vestibular function. Symptoms include facial pallor, cold sweating, stomach awareness, anorexia, vomiting, nausea, headache

On Earth, venous return from the head, neck and upper trunk is supported by gravity. Unlike the lower half of the body, the veins draining this region do not have valves and lack muscular contraction. In space, there is reduced arterial blood supply and venous flow from the eye. This increases the venous pressure and filtration at the capillaries causing an increase in both intracranial pressure and IOP [15].

Extended exposure to microgravity leads to a loss of bone and muscle mass due to its reduced use and perfusion changes. Inadequate nutrition and stress are additional reasons that lead to muscle atrophy [2]. Weight bearing bones: lumbar spine, pelvis, femoral neck and trochanter, and calcaneus and postural muscles:

In addition to absence of gravitational loading, decreased Vitamin D production—partly due to low levels of sunlight—leads to decreased calcium fixation in bones and reabsorption in kidneys. Higher ambient levels of carbon dioxide, leading to respiratory acidosis also contribute to bone loss [2, 15] Increase in urinary calcium coupled with a reduction in diuresis and decreased fluid intake increases

Microgravity induced changes in the lungs have been the subject of much interest for decades. The ventilation to perfusion ratio attains equilibrium in the absence of gravity [15, 16]. There is an increase in the total alveolocapillary surface which in turn improves the lung diffusing capacity [16]. Gas exchange in space does not undergo a substantial change but there is reduced oxygen consumption and carbon dioxide production. This is attributed to a reduced physical activity in space

back, abdominal wall, lower limbs are most commonly affected [2, 24].

**198**

and change in the ventilation to perfusion ratios between the upper and lower lung regions. These factors lead to an overall reduction in the metabolic rate [15].

Changes in the thoracoabdominal compliance is advantageous to the pulmonary function [16].

Microgravity can cause weakening of the respiratory muscles leading to a reduced rib cage expansion. Thus, there is an increased contribution of the abdomen to tidal volume [28]. Intra-abdominal pathology and subsequent intraabdominal hypertension is important to providing life support and mechanical ventilation. However, it has been demonstrated that intra-abdominal gas insufflation during laparoscopic surgery in space and the subsequent intra-abdominal hypertension is made better by the absence of gravity [15, 16].

It has been suggested that changes in the respiratory system are similar to those that occur to individuals on prolonged bed rest and are anatomical in nature [15]. These typically occur over several weeks. There is a significant reduction in tidal volume [15, 16] and residual volume [29]. Vital capacity and forced vital capacity reduce initially followed by subsequent recovery. Functional residual capacity (FRC) reduces by 500 ml and remains at that level for the remainder of the period in space [29, 30]. Peak inspiratory and expiratory flows are also not significantly altered. However maximum inspiratory pressure significantly reduces, while the maximum expiratory pressure (MEP) at total lung volume initially reduces at month 2 and month 4, but recovers by month 6 of being in microgravity. The MEP at FRC however is not affected [15].

#### **4.7 Immune system**

Immune system dysregulation occurs in space. High levels of physical and psychological stress—immediately before and after space flight— physiological stress, isolation, confinement, disrupted circadian rhythms are some of the contributing factors to immune system dysregulation [2]. Additionally, increase in levels of glucocorticoids and catecholamines, may also contribute to change in the immune system [3, 31]. Various studies have demonstrated that lack of gravity impairs the signalling pathways that are necessary for early T-cell activation. This leads to changes in the organisation of the cytoskeleton and microtubule organising centres [2].

Immune system dysregulation can lead to an increased incidence of hypersensitivities, autoimmunity, allergies, infectious diseases, latent viral reactivation and even malignancies [3].

Microbes undergo several changes in their characteristics in space. Notably, bacteria cultured on board have increased pathogenicity [32]. The microorganisms present in the human body, are transmitted easily between persons, in such confined habitats [3].

#### **4.8 Gastrointestinal motility**

Gastrointestinal motility is reduced in space especially in the first 72 hours. It has also been observed that the gastric content pH decreases [16].

#### **4.9 Weight loss**

Astronauts experience a weight loss of up to 5% after a 6 month stay on the International Space Station (ISS). This is explained by a mismatch between caloric intake and caloric expenditure [16, 33, 34].

### **4.10 Psychological effects**

Confinement and isolation in constrained spaces, for extended periods of time, affects one's psychological health. Even with screening, training, and support; behavioural issues, cognitive conditions, and psychiatric disorders among crew members, is to be expected. Decline in mood, cognition and morale can occur. Sleep disorders due to changes in their circadian rhythms is also quite common [2, 3].

Extended exposure to stress, isolation and changes in circadian rhythm can have a psychological impact on astronauts. Cognitive impairment, sleep disorders, psychosomatic symptoms, anxiety and even depression can occur [7].

Personnel skills like team coordination, communication, logistics, etc. and technical skills like troubleshooting equipment, use of safety equipment, orientation, etc. contribute to the health and safety of astronauts. Selection of suitable crew, training and maintenance of skills during the mission, is important. Therefore, medical and psychological benchmarks for crew-member selection ought to be very high [7].

#### **4.11 Exposure to radiation**

Space travel presents the additional risk of exposure to harmful radiation. On Earth, we are shielded from cosmic radiation by the Earth's magnetic field and its atmosphere. However, on a space station astronauts are exposed to up to ten times the radiation they are exposed to while on Earth. Radiation in space can cause radiation sickness and degenerative tissue disease, among many other serious issues [3].
