Predictors of nocturnal oxygen desaturation in pulmonary arterial hypertension

Background:Sleep may be associated with significant respiratory compromise in patients with lung disease and can result in hypoxia. In patients with pulmonary arterial hypertension (PAH), nocturnal desaturation may not be reflected in daytime evaluations of oxygenation and can lead to worsening pulmonary hemodynamics. The study was conducted to determine the prevalence and significance of nocturnal oxygen desaturation in patients with PAH.Methods:A cross-sectional study conducted at the Cleveland Clinic. Patients were followed up at our institution except for the overnight oximetry study done at home. Data regarding degree of nocturnal desaturation, demographics, hemodynamics, pulmonary function, and functional capacity were collected.Results:Forty-three patients (mean age, 47.9 ± 13.5 years [± SD]; 36 women and 7 men) underwent nocturnal oximetry. The etiology of PAH included idiopathic PAH (88%) and PAH associated with connective tissue diseases (12%). The majority of patients were New York Heart Association functional class II (42%) or III (53%). Thirty patients (69.7%) spent > 10% of sleep time with oxygen saturation by pulse oximetry < 90%. Desaturators were older (p = 0.024) and had higher hemoglobin (p = 0.002). Sixteen of 27 patients (59%) without desaturation < 90% during a 6-min walk test were nocturnal desaturators. Nocturnal desaturators had higher brain natriuretic protein (p = 0.004), lower cardiac index (p = 0.03), and higher mean right atrial pressure (p = 0.09), mean pulmonary artery pressure, and pulmonary vascular resistance. On echocardiography, desaturators were more likely to have moderate or severe right ventricular dilation (p = 0.04) and pericardial effusion. Only one patient had significant sleep apnea.Conclusions:Nocturnal hypoxemia is common in PAH patients and correlates with advanced pulmonary hypertension and right ventricular dysfunction. Approximately 60% patients without exertional hypoxia had nocturnal desaturation. Overnight oximetry should be considered in the routine workup of PAH patients who do not demonstrate exertional desaturation.     

Oxygen Saturation and Hemoglobin A Content in Patients with Sickle Cell Disease Undergoing Erythrocytapheresis

Abstract: Severe hypoxia occurs in patients with acute chest syndrome, and erythrocytapheresis has been shown to improve oxygenation. Patients with sickle cell anemia also have decreased baseline oxygen saturation values, but the effect of erythrocytapheresis on steady‐state oxygenation has not been well studied. We investigated the changes in oxygen saturation versus hematocrit, fraction of hemoglobin A, and transfusion volume during 71 prophylactic erythrocytapheresis procedures performed in 5 stable patients with sickle cell anemia. Each patient had a history of either acute chest syndrome or stroke, but no serious events occurred while enrolled in the chronic exchange program. The oxygen saturation improved from 1% to 6% during erythrocytapheresis in each of our patients (p < 0.001) regardless of preprocedure saturation level or total hematocrit. We have shown that decreased baseline oxygen saturation in sickle cell disease is related to abnormal hemoglobin S levels, and oxygen saturation can be improved with erythrocytapheresis, independent of any change in the total hematocrit.     

Auricall. A new device for a non-invasive, wireless, continuous monitoring of oxygen saturation and heart rate in patients with heart failure

Sleep apnoea syndrome is frequent in patients with heart failure and associated with a worse prognosis. We evaluated a new device (Auricall®) for non-invasive, continuous recording of oxygen saturation (SpO₂) and heart rate (HR) in patients with heart failure. We studied 20 patients (mean age 48.43 ± 14.4 years, NYHA class II–III). All patients were requested to carry the device for at least 36 h and to write a diary during the recording time. Satisfactory recording of SpO₂ and HR was possible to obtain in 18 of 20 patients. Indeed 9 out of 18 patients showed significant periodic changes in SpO₂ during sleep. Therefore, Auricall® is a useful tool to non-invasively monitor SpO₂ and HR in patients with heart failure and to detect breathing disorders in these patients.     

Modifying track layout from straight to circular has a modest effect on the 6-min walk distance

BACKGROUND: The protocol used for the 6-min walk test (6MWT) influences its results. The only study to examine the effect of modifying track layout performed a retrospective analysis and concluded that institutions using continuous tracks yield greater distances than those using straight tracks. Agreement between the distances measured on different tracks could not be examined. We evaluated the effect of modifying track layout on walk distance and examined the agreement and repeatability of distances measured on different tracks. METHODS: In a prospective, randomized, cross-over study, 27 COPD subjects (FEV(1), 38 +/- 14% [mean +/- SD]; 15 men) attended three separate test sessions, completing six 6MWTs. To familiarize all subjects with both tracks, the first two sessions comprised two 6MWTs on either a circular or straight track. During the final session, each subject was tested once on the straight and once on the circular track. RESULTS: The distance walked on the circular track exceeded the straight track by 13 +/- 17 m (p < 0.001). The limit of agreement between tracks was 33 m. Coefficient of repeatability values when the test was completed on different days for the straight and circular tracks were 51 m and 65 m, respectively. CONCLUSIONS: When evaluating changes in 6-min walk distance in groups of patients, track layout should be standardized. However, the effect of modifying track layout on an individual's walking distance is small compared to their daily variability in walk distance. Therefore, standardizing track layout for any given individual may be inconsequential when evaluating the change in distances from tests performed on different days.     

Hypertrophic cardiomyopathy associated with sleep apnea: serious implications and cogent management strategy

Obstructive sleep apnea (OSA) affects an estimated 20 million adult Americans and is present in a large proportion of patients with hypertension and in those with other cardiovascular disorders, including hypertrophic cardiomyopathy (HCM). This review seeks to highlight concepts and evidence important to understanding the interactions between OSA and HCM, with particular attention to more recent advances in patient-oriented research. Studies of patients with HCM have found the prevalence of sleep-disordered breathing to range from 40 to 80%. Increased sympathetic activity, impaired vagal activity, increased afterload, insulin resistance and endothelial dysfunction have been proposed as potential mechanisms for the association. Specific questions include whether OSA is important in unmasking symptoms in hitherto undiagnosed patients with HCM, whether OSA in patients with established HCM accelerates disease progression and whether treatment of OSA results in clinical improvement, fewer cardiovascular events and reduced mortality. Because obesity, cardiovascular disease, metabolic syndrome, and diabetes are often present in patients with OSA, it can be difficult to attribute abnormalities evident in the sleep apnea patient with HCM to the effects of OSA, the effects of HCM or synergies between these conditions. Although further research is needed to answer these specific questions, recent investigations have clearly shown the coexistence of OSA and HCM, as well as elucidated the contribution of heightened sympathetic nerve activity in OSA to drug-refractory symptoms and worsening left ventricular outflow tract obstruction. This review aims to highlight the current literature available on the association of OSA and HCM, provide directions for future research and summarize the key features related to this association based on the authors’ best understanding and experience.     

The effect of acute normovolemic haemodilution on cerebral oxygenation

Acute normovolemic haemodilution (ANH) may cause an imbalance in cerebral oxygen metabolism because it decreases the arterial oxygen content. This study was designed to investigate the effect of ANH on cerebral oxygenation. By using cerebral oximetry, the regional cerebral oxygen saturation (rSO2) was monitored during ANH in 26 patients without systemic illness (initial haematocrit = 42 +/- 1%). The rSO2 did not show a significant change until the Hct reached >30%. However, it decreased significantly thereafter to reach 88% of the baseline value when the ANH was completed with a Hct value of 24 +/- 1% (before ANH; 71 +/- 6% vs. after ANH; 62 +/- 4%, p < 0.01). In conclusion, an ANH can lead to a reduction in cerebral oxygenation when a patient's Hct goes below 30%.     

Effect of obesity and glycated hemoglobin on oxygen saturation in ambulatory type 2 diabetic individuals: A pilot study

AimsTissue hypoxia is an important contributor to diabetic complications. Glycation of hemoglobin (Hb) and obesity are major determinant of oxygen saturation (SpO2) in blood. Hence, the present study was planned to evaluate the effect of obesity on SpO2 in a wide range of glycated hemoglobin (HbA1c) levels in ambulatory type 2 diabetic patients.Material and methodsA cohort of 60 subjects irrespective of diabetic status were recruited and clustered in group I (HbA1c <6.5) and group II (HbA1c ≥6.5) depending on HbA1c. Anthropometry and routine biochemical parameters were measured. HbA1c (%) were estimated by high performance liquid chromatography (HPLC) respectively. SpO2 (%) levels were measured by pulse oximetry. Pearson correlation, bivariate regression and student ‘t’ test were used for statistical analysis.ResultsBlood concentration of HbA1c was <6.5 in 29 participants and ≥6.5 in 31 participants. Plasma fasting and post prandial glucose, HbA1c as well as Hb levels were significantly (p < 0.50) higher in diabetics as compared to non diabetics. Waist circumference (WC) (r = −400; p = 0.026) and body mass index (BMI) (r = −381; p = 0.034) showed a significant negative correlation with SpO2 in diabetic patients. On adjusting HbA1c in group II, SpO2 was found to independently and inversely associated with WC (p = 0.042) and BMI (p = 0.049).ConclusionsObesity was found to be a strong independent contributor to reduction in oxygen carrying capacity in ambulatory type 2 diabetic subjects. However there is no effect of glycated Hb on SpO2 in the same population.     

Chronic performance of a subcutaneous hemodynamic sensor

Background: A subcutaneous photoplethysmography (PPG) sensor uses light to detect changes in vascular volume from a location outside the bloodstream. Incorporation into a chronically implanted device, such as a pacemaker or an implantable cardioverter defibrillator, may facilitate therapy optimization and disease monitoring by providing continuous assessment of hemodynamic function and arterial oxygen saturation. However, performance of a chronically placed subcutaneous sensor has not been established. Methods: Six dogs were implanted with 2-4 PPG sensors subcutaneously in the neck or posterior thorax. Half of the sensors were directed toward deep tissue and half toward overlying cutaneous tissue. Each sensor contained a red and an infrared light emitting diode, a photodetector, and supporting electronics, which were encapsulated in epoxy and attached to a transcutaneous connector. Data were collected at implant and every 3 ± 1 days for 4-9 months starting 3 weeks postimplant. At explant, the fibrous encapsulation was histologically analyzed. Results: A minimally to moderately neovascularized encapsulation formed over all sensors, consisting of fibrous and granulation tissue. Higher cardiac pulse amplitudes and direct current (DC) components were recorded in sensors oriented toward deep tissue, but no significant difference between orientations was found in respiratory wave amplitude. Cardiac pulse amplitude, respiratory wave amplitude, and DC component amplitude, as recorded by the sensor, did not significantly change over time. Conclusions: Despite fibrous encapsulation of PPG sensors, cardiac pulses and respiratory waves could easily be measured throughout the study and remained constant over time. These results suggest suitability of subcutaneous PPG technology for chronic applications. (PACE 2012; 35:919-926).