OXYHEMOGLOBIN DESATURATION AND ABERRANT CARBON-DIOXIDE HOMEOSTASIS DURING ELECTRICALLY STIMULATED EXERCISE IN A VENTILATOR-DEPENDENT TETRAPLEGIC PATIENT

This single-subject case examined oxyhemoglobin saturation and alveola r end-tidal carbon dioxide levels in a ventilator-dependent tetraplegi c patient undergoing electrical stimulation cycle ergometry. When exer cising with a closed tracheostomy cuff under resting ventilator settin gs (resting intermittent mandatory ventilation; frequency = 6breaths/m in, tidal volume 83.3mL, minute ventilation = 5L/min), his oxyhemoglob in saturation decreased from 100% to 92%, while alveolar end-tidal car bon dioxide increased linearly to 47mmHg. These undesirable changes we re corrected under adjusted intermittent mandatory ventilation conditi ons (frequency = 12breaths/min, tidal volume = 83,3mL, minute ventilat ion = 10L/min), during which oxyhemoglobin saturation remained above 9 8% and the alveolar end-tidal carbon dioxide trend resembled that of v entilator-independent tetraplegic individuals undergoing the same exer cise. Because the subject's heart rate was higher under adjusted venti lation conditions, these responses may have been caused by augmented v enous return resulting from greater abdominothoracic pumping at the hi gher breathing frequency. These findings support the need to modify ve ntilator settings in ventilator-dependent tetraplegic persons while un dergoing exercise to maintain oxyhemoglobin saturation and carbon diox ide homeostasis. (C) 1998 by the American Congress of Rehabilitation M edicine and the American Academy of Physical Medicine and Rehabilitati on.