Ambulatory Monitoring of Oxygen Saturation in Chronic Lung Disease: Optimizing Long-Term Oxygen Therapy:

Improving pulse oximetry accuracy by removing motion artifacts from photoplethysmograms using relative sensor motion: a preliminary study

To expand applicability of pulse oximetry in low-acuity ambulatory settings, the impact of motion on extracted parameters as saturation (SpO2) and pulse rate (PR) needs to be reduced. We hypothesized that sensor motion relative to the skin can be used as an artifact reference in a correlation canceller to reduce motion artifacts in photoplethysmograms (PPGs), in order to improve SpO2 and PR measurements. This has been proven true in in vivo measurements, where forehead PPGs have been obtained while subjects are walking on a treadmill and relative sensor motion has been measured via self-mixing interferometry. By using relative motion in a normalized least mean square algorithm, the standard deviation of SpO2 and PR errors is on average reduced by 31 % and 13 %, respectively.

The relationship of the BODE index to oxygen saturation during daily activities in patients with chronic obstructive pulmonary disease

BACKGROUND

The frequency of oxygen desaturation during daily activities in chronic obstructive pulmonary disease (COPD) is poorly defined. The BODE index predicts survival in COPD. The purpose of this study was to determine the relationship between BODE scores and oxygen saturation during daily activities.

METHODS

Seventy-eight patients with COPD (FEV(1) = 37%) underwent ambulatory oximetry and activity monitoring. We defined four activity categories: Walking, Slow-Intermittent-Walking (SIW), Active-Not-Walking (ANW), and Rest. We quantified oxygen desaturation during activity using a desaturation index (DSI = % time oxygen saturation <90%). BODE scores were categorized into three groups: group I (0-3), II (4-6), and III (7-10).

RESULTS

The percentage of patients demonstrating oxygen desaturation (DSI ≥ 10%) during each activity was 55% for Walking, 35% for SIW, 15% for ANW, and 28% for Rest. There was a strong association between BODE score and desaturation for Walking and SIW. During Walking, 21, 44, and 86% of patients in BODE groups I, II, and III, respectively, demonstrated desaturation. The DSI for Walking and SIW was increased in patients in BODE groups II and III compared to group I (P < 0.006, P < 0.007, respectively). BODE score was also linked to long-term oxygen therapy (LTOT) usage; the majority of patients not on LTOT (89%) had a BODE score <7. The majority of patients on LTOT (84%) demonstrated desaturation during Walking, but 42% of patients not on LTOT also demonstrated desaturation. In this subgroup of patients not on LTOT, all patients with a BODE score ≥ 7 demonstrated desaturation during Walking.

CONCLUSIONS

The link between the BODE index and oxygen desaturation during daily activities suggests that desaturation is linked to disease severity. Our data suggest that patients with a BODE score ≥ 7 should be evaluated for desaturation during daily activities. Use of the BODE index to screen for exertional desaturation may have value as a tool that can lead to the earlier identification of patients who may be candidates for LTOT.

Dyspnea

When evaluating a dyspneic patient in the office, a quick initial assessment of the airway, breathing, and circulation, while gathering a brief history and focused physical examination are necessary. Most often, an acute cardiopulmonary disorder, such as CHF, cardiac ischemia, pneumonia, asthma, or COPD exacerbation, can be identified and treated. Stable patients who improve can be sent home, but those in acute distress with unstable or impending unstable conditions need to be transferred emergently to definitive care. Because of the difficult logistics involved in attempting to work up an outpatient for new onset of SOB, some patients will need to be transferred to the nearest ED for a definitive diagnosis.