Diagnosing the cause of hypoxemia and dyspnea can be complicated in complex patients with multiple co-morbidities. This Case Study in Physiology describes an obese man admitted to the hospital for relapse of acute lymphoblastic leukemia, who experienced progressive hypoxemia, shortness of breath, and dyspnea on exertion during his hospitalization. After initial empirical treatment with diuresis and antibiotics failed to improve his symptoms, we applied a novel, recently described physiological method to estimate the arterial partial pressure of oxygen from the peripheral saturation measurement, and calculate the alveolar-arterial oxygen difference to discern the source of his hypoxemia and dyspnea. Using basic physiological principles, we describe how hypoventilation, anemia, and the use of a beta-blocker and furosemide, collaborated to create a "perfect storm" in this patient that impaired oxygen delivery and limited utilization. This case illustrates the application of innovative physiology methodology in medicine and provides strong rationale for continuing to integrate physiology education in medical education.
Chronic intermittent hypoxia, CIH, is a feature of sleep apnea widely used in research to mechanistically examine the physiological effects of sleep apnea. These mechanistic studies commonly utilize mice as the study model. In room air, mice experience periodic apneas and arterial oxygen desaturations. Activation of the carotid body could stabilize breathing and decrease these events. Therefore, we hypothesized that C57BL/6J mice experience fewer hypoxic events with decreasing FIO2.We placed 6 C57BL/6J mice (3 male, 3 female) in an Emka® unrestrained barometric plethysmograph and measured pulse oximetry using the STARR LifeSciences MouseOx® Plus system. The mice were exposed to different levels of FIO2 for 10 minutes each: 0.21, 0.15, 0.12, 0.09, 0.30 ± 0.01. We defined a hypoxic event as 3% deviation from the average oxygen saturation at each FIO2. Mice did not show fewer hypoxic events when exposed to increasing levels of hypoxia. In fact, mice experienced more hypoxic events at 0.15 than 0.21 and 0.30 FIO2 (P<0.05). Mice also experienced more hypoxic events at 0.12 than at 0.30 FIO2. Additionally, we found that hypoxic event nadir SpO2 was significantly lower at all FIO2 levels when compared to 0.21 FIO2. Hypoxic events at all FIO2 levels had significantly lower average SpO2 compared to 0.21 FIO2. No change was observed for average SpO2 for hypoxic events at 0.30 FIO2 relative to 0.21 FIO2. Contrary to our hypothesis, intermittent hypoxic events are not stabilized by exposure to a hypoxic environment. Future work will evaluate this in other mouse strains. 1R56HL152365 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
Chamber exposures are commonly used to evaluate the physiological and pathophysiological consequences of intermittent hypoxia in animal models. Researchers in this field use both commercial and custom-built chambers in their experiments. The purpose of this Cores of Reproducibility in Physiology paper is to demonstrate potential sources of variability in these systems that researchers should consider. Evaluating the relationship between arterial oxygen saturation and inspired oxygen concentration, we found that there are important sex-dependent differences in the commonly used C57BL6/J mouse model. The time delay of the oxygen sensor that provides feedback to the system during the ramp-down and ramp-up phases was different, limiting the number of cycles per hour that can be conducted and the overall stability of the oxygen concentration. The time to reach the hypoxic and normoxic hold stages, and the overall oxygen concentration, were impacted by the cycle number. These variables were further impacted by whether there are animals present in the chamber, highlighting the importance of verifying the cycling frequency with animals in the chamber. At ≤14 cycles per hour, instability in the chamber oxygen concentration did not impact arterial oxygen saturation but may be important at higher cycle numbers. Taken together, these data demonstrate the important sources of variability that justify reporting and verifying the target oxygen concentration, cycling frequency, and arterial oxygen concentration, particularly when comparing different animal models and chamber configurations.
Diagnosing the cause of hypoxemia and dyspnea can be complicated in complex patients with multiple co‐morbidities. This Case Study in Physiology describes an obese man admitted to the hospital for relapse of acute lymphoblastic leukemia, who experienced progressive hypoxemia, shortness of breath, and dyspnea on exertion during his hospitalization. After initial empirical treatment with diuresis and antibiotics failed to improve his symptoms, we applied a novel, recently described physiological method to estimate the arterial partial pressure of oxygen from the peripheral saturation measurement, and calculate the alveolar‐arterial oxygen difference to discern the source of his hypoxemia and dyspnea. Using basic physiological principles, we describe how hypoventilation, anemia, and the use of a beta‐blocker and furosemide, collaborated to create a “perfect storm” in this patient that impaired oxygen delivery and limited utilization. This case illustrates the application of innovative physiology methodology in medicine and provides strong rationale for continuing to integrate physiology education in medical education.
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