Cardiovascular Variability and Respiratory Influences under Hyperbaric Conditions Introduction • Known affects of atmospheric pressures greater than 1 atm o Heart rate variability  Health  Unhealthy o Affect on blood O2 saturation o Changes in respiration • Recreational scuba diving and common medical treatments o Roughly 4 atm at 30 m (in sea water) o 2.5-3 atm used in medical treatments o What does this do to the function of the heart  Are there any long term effects  Dangers of scuba diving  “Normal” reaction to increased atmospheric pressure • Unknowns o Is controlled breathing linked to HRV o Additional information for scuba divers • Outline of paper o Background info  Brief history of scuba diving  Brief history of hyperbaric medical treatments o Methods used for studying normal response to pressure  Professional divers  Controlled breathing o Results of study  Contradict previous study  Increased Vagal tone o Discussion  Possible problems with study  Indicative of normal medical treatment response? o Conclusion Background • Heart is capable of functioning under significantly increased pressures o Depths of 100 m below sea level o 3 atm  Used in medical treatments, CO poisoning, deep wounds… • What is challenging about this stress o Deep sea divers  Oxygen toxicity • Slows breathing  Increased outside pressure on heart o Medical treatments  Hyperbaric hyperoxia induces bradycardia  Hyperbaric air (O2 21% at ≥ 2.5 atm) • What affects do these have on the heart and respiration• Method of analysis o 4 min ECG recordings o HRV- how it is calculated and its purpose  HF and LF Methods (Lund2000) • Male professional divers o Controlled breathing 15 breaths per min o Followed time table used in hyperbaric oxygen (HBO) medical treatments • 4 minute ECGs following reaching a level of pressure o After 30 min of rest at 1 atm o After reaching 2.5 atm for 30 min o After exposure to 2.5 atm for 55 min o After ascending to 1.6 atm o After decompression • Study done for both 100% O2 and 21% O2 (normal air) • Statistical analysis of HRV Results (Lund2000) • Heart rate decreased with increased pressure o Results similar for both cases • HRV increased for both cases o HRV greater for 100% O2  Greater HF (high frequency) component  Greater LF (low frequency) component • Arrhythmias o Increased QT and PQ durations  Due to vagal response Discussion: • What triggers a parasympathetic response to increased pressure? o Increased outside pressure on the heart o Increased O2 concentration in blood o Respiration (maintained constant across study) • Mechanisms o Reduced venous flow  Shift of pressure-flow graphs (Aldea2000)  Excess O2 due to increased pressure o Slower heart rate  Reduced venous return  Increased vagus response • Increased O2 in blood • Increased outside pressure on heart  Effective reduction in ventricular capacity o Controlled breathing  Probably reduced volume• Weakness o Controlled breathing  Although compensated in analysis, affects other mechanisms  Not typical of patients receiving hyperbaric treatments o Professional Divers  Trained response to exposure to pressure  Developed compensatory mechanisms  Much lower pressures than what professional divers experience  Potential panic likely to be seen in patients not present • Questions o How would this change with less experienced divers o What would change without controlled breathing  Less obvious changes in HRV • Lungs would help compensate (i.e. slower respiration