|Ahead of print publication
Effect of submarine microclimate on respiratory physiology of submariners: An observational study
Vivek Verma1, Abhishek Sharma2, N Anand3
1 Officer-In-Charge, School of Naval Medicine, INHS Asvini, Mumbai, Maharashtra, India
2 Graded Spl (Surgery), Department of Surgery, INHS Asvini, Mumbai, Maharashtra, India
3 Officer-In-Charge, SHO, Kochi, Kerala, India
|Date of Submission||27-Mar-2020|
|Date of Decision||08-May-2020|
|Date of Acceptance||25-Nov-2020|
|Date of Web Publication||01-Apr-2021|
SHO, Kochi, Kerala
Source of Support: None, Conflict of Interest: None
Introduction: A few personnel feel more tired staying and working inside submarine, as compared to ashore/outdoor spaces, or even onboard afloat platforms (ships). The microclimate onboard underwater platforms play a vital role in determining the respiratory physiology parameters of personnel onboard. There exists a felt need for deeper evidence in this regard. Aims and Objectives: This study is an effort to analyze if there exists any relationship between concentrations of respiratory gases (such as oxygen and carbon dioxide) and other parameters of submarine microclimate, on the respiratory physiology parameters (such as respiratory rate [RR] and SpO2) of personnel onboard underwater platforms. The difference in concentrations of oxygen and carbon dioxide in exhaled air of personnel both inside and outside submarine was also studied. Any difference between smokers and nonsmokers regarding this parameter was also evaluated. Materials and Methods: The study was carried out on thirty healthy volunteers posted onboard a submarine. Concentrations of oxygen and carbon dioxide in the atmosphere, as also the exhaled air, were measured using a digital gas analyzer. Humidity, temperature, and oxygen saturation were measured using digital meters. The values both inside and outside were recorded and compared. Results: There was a statistically significant difference in the temperature, humidity, and level of CO2 inside and outside the submarine. There was no statistically significant difference in level of oxygen in atmosphere, oxygen and carbon dioxide in exhaled air, RR, and SPO2 level inside and outside the submarine. Conclusion: The corrected effective temperature inside a submarine is to be measured periodically and maintained in the comfort zone. The level of CO2 should be maintained close to environmental levels.
Keywords: Respiratory Physiology, Submarine Microclimate, Corrected Effective Temperature(CET)
| Introduction|| |
The microclimate onboard a submarine is well controlled, both in harbor and at sea. This is effected by periodic ventilation, air-conditioning, and regeneration of oxygen as and when required. The temperature, humidity, and the concentration of oxygen (O2), carbon dioxide (CO2) onboard and other gases are maintained within the normal limits (in the comfort zone).,
Notwithstanding such controlled maintenance, a few personnel onboard underwater platforms reported a feeling of tiredness/early fatigue while working and staying inside a submarine, as compared to working inshore office/outside in the open. It is postulated that the possible causes for such feeling of exhaustion could be: decreased oxygen (O2), increased concentration of certain gases like carbon dioxide (CO2), carbon monoxide (CO), chlorine (Cl2), hydrogen sulphide, and Freon inside a submarine. Increased humidity and temperature inside these vessels are also postulated to be other determinants of such subjective feeling., The other probable factors may be psychological stress, noise, inadequate lighting, and vibration due to machinery.
However, studies exploring the relationship between submarine microclimate and respiratory parameters of personnel working and staying thereon are few and far between. This study is an effort in this direction to address the knowledge gap on the link between the two.
Aims and Objectives
The aim of the study was to explore the relationship between microclimate onboard submarine and various respiratory parameters of personnel onboard. The objectives were to compare the values of related environmental parameters (namely temperature, humidity, oxygen, arbon dioxide, and other gases) both inside and outside the submarine. The second objective was to study any difference in respiratory physiology parameters (namely respiratory rate [RR], saturation of peripheral oxygen (SPO2), and concentrations of exhaled carbon dioxide and oxygen) inside and outside the submarine. It was also envisaged to study the difference between smokers and nonsmokers with respect to these respiratory physiological parameters.
| Materials and Methods|| |
The study was carried out on 30 healthy volunteers posted onboard a submarine. After obtaining requisite administrative approval and informed consent, study subjects were divided into five groups of six personnel, each depending on their age (which varied between 22 years and 48 years). Humidity and temperature were measured using a digital meter. The concentrations of oxygen and carbon dioxide in the atmosphere and exhaled air were measured using a digital gas analyzer (Technovation: ECR1). The levels of other gaseous elements were measured using Uniphos tubes and pumps. All measurements were done at the duty watchposts of respective volunteers.
RR was measured by counting abdominal movement manually. SPO2 was measured using a multiparameter monitor (Mindray). One reading each was taken inside and outside the submarine for all the specified parameters. The readings were taken on the same day for a group of personnel approximately at the same time of the day after the patient was sitting comfortably for 5 min. To mitigate the effect of potential confounding factors, it was ensured that the participants did not consume food/beverages, did not exert, and did not smoke before the time of recording the parameters. The findings were recorded on an Excel sheet and analyzed using Epi Info software. Unpaired t-test was used to compare readings of outside environment with inside and also between smokers and nonsmokers.
| Results|| |
The mean age of the study population was 28.2 years. The population was equally distributed between five different watchposts in different compartments. The results of various environmental parameters are enumerated in [Table 1].
The results of various respiratory physiological parameters are enumerated in [Table 2].
The results of various physiological parameters were compared between smokers and nonsmokers and the results are enumerated in [Table 3].
|Table 3: Difference of physiological parameters between smokers and nonsmokers|
Click here to view
| Discussion|| |
In the newer underwater platforms of the Indian Navy, keeping in mind the tropical climate and water conditions, a number of air conditioning units have been installed to maintain the temperature in the comfortable and cool zone. However, the concept of measuring corrected effective temperature (CET) and humidity inside a submarine is evolving. Guidelines have to be formulated and watchkeepers are to be issued instructions to maintain the CET instead of only temperature in the comfort zone range of between 20°C and 27°C. Increased relative humidity (RH) can lead to a feeling of discomfort and reduce the efficiency of submarine crew. However, if CET is measured and maintained in the comfort zone range, then the effect of RH will also be addressed.
The mean concentration of oxygen inside was significantly lower as compared to outside; however, this minor reduction did not lead to any detectable physiological stress to the individuals. As per measured parameters, the CO2 concentration inside was almost five times as compared to outside. Although CO2 inside was still in the normal range as recommended for submarine atmosphere and can be adjusted for by slightly increased RR, it may be one of the reasons for early tiredness due to hyperventilation and increased work of breathing.
No significant increase in RR was seen while a person is at rest in our study. However, when a person carries out manual work inside a submarine, this may lead to a higher increase in RR, as compared to breathing CO2 at atmospheric concentration. The mean concentration of oxygen in exhaled air outside was higher as compared to inside. The reduced concentration of inhaled oxygen, when a person is inside the submarine and increased absorption of oxygen thereby, may be a possible reasons for this. The mean concentration of CO2 in exhaled air was higher inside; however, this difference was statistically not significant. A higher concentration of inhaled CO2 inside the submarine may be the reason for this observation as it may be due to increased work of breathing.
RR of personnel at rest while inside the submarine was similar to that on the outside, with no statistically significant difference. However, in case of exertion, there may be a greater increase in RR as compared to outside. The peripheral saturation of oxygen (SPO2) inside was marginally lower inside as compared to outside, which shows that the reduced concentration of oxygen inside the submarine most likely did not lead to any significant difference in the SPO2 at rest.
The mean concentration of oxygen in expired air (O2Exp) in smokers (outside and inside) was higher as compared to nonsmokers. This may be due to reduced extraction/diffusion of oxygen into pulmonary circulation in smokers as compared to nonsmokers., The mean concentration of CO2Exp in smokers was higher both outside and inside as compared to nonsmokers. The peripheral saturation of oxygen (SPO2) in smokers inside reduced more as compared to nonsmokers which did not change much. This may be due to reduced diffusion of oxygen into pulmonary circulation in smokers as compared to nonsmokers.
The levels of CO, H2S, oxides of nitrogen, hydrocarbons, chlorine, and Freon were found to be below detectable levels when measured using available Uniphos tubes. Various countries have variable values for gaseous levels for indoor air quality., The levels recommended onboard submarines by various countries are not available freely in the public domain; however, it is recommended that these be maintained as per the current WHO guidelines for closed spaces onboard submarines in peacetime scenario. These levels should be exceeded only in exceptional operational requirements.
| Recommendations and Conclusion|| |
The temperature inside the submarine was comfortable; however, the RH was slightly higher. To achieve optimum efficiency, the CET instead of temperature only should be measured inside the submarine four hourly and kept in the comfort zone. The oxygen and carbon dioxide levels inside the submarine, though found different as compared to outside, did not lead to any significant measurable increase in RR or SPO2 while at rest. The CO2 levels may be lowered by dynamic and cyclical changes in the ventilation schedule. The CO2 and O2 levels inside the submarine should be kept as close to environmental levels as possible. In future studies, more extensive study measuring ABG, urine pH, index of tiredness, and dyspnea index.
Limitations of the study
A number of factors can have a bearing on the respiratory parameters measured, of which only a few could be explored. Further, more direct indicators of effect of oxygen and carbon dioxide, such as arterial blood gas analysis, Urine pH could not be measured in this study due to nonavailability of these equipments onboard. Dyspnea index and oxygen–carbon dioxide diffusion can be affected by type of food; hence, these parameters were not considered.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
World Health Organization, editor. WHO Guidelines for Indoor air Quality: Selected Pollutants. Copenhagen: WHO; 2010. p. 454.
National Research Council 2009. Emergency and continuous exposure level for selected chemical pollutants. Vol. 3. Washington DC: National Academic Press; 2009.
Verma V. To study different pollutants in submarine atmosphere during a long submersion: Armed Forces Medical Research Committee project report ; 3190/2003.
Corradi M, Mutti A. Exhaled breath analysis: From occupational to respiratory medicine. Acta Biomed 2005;76 Suppl 2:20-9.
Chabal S, Welles R, Haran FJ, Markwald R. Effect of sleep and fatigueon teams in a submarine environment. Undersea Hyperb Med 2018;45:252-72.
Koteswara Rao MV. Environment in submarines. New Delhi: Defence Research & Development Organisation, Ministry of Defence (DRDO Monographs/Special Publications Series); 2001. p. 124.
Kang J, Song YM. The association between submarine service and multimorbidity: A cross-sectional study of Korean naval personnel. BMJ Open 2017;7:e017776.
Corradi M, Pignatti P, Manini P, Andreoli R, Goldoni M, Poppa M , et al
. Comparison between exhaled and sputum oxidative stress biomarkers in chronic airway inflammation. Eur Resp J 2004;24:1011-7.
[Table 1], [Table 2], [Table 3]