The complement system is a major constituent of the innate immune system. It not only bridges innate and adaptive arms of the immune system but also links the immune system with the coagulation system. Current understanding of the role of complement has extended far beyond fighting of infections, and now encompasses maintenance of homeostasis, tissue regeneration, and pathophysiology of multiple diseases. It has been known for many years that complement activation is strongly pH sensitive, but only relatively recently has the physiological significance of this been appreciated. Most complement assays are carried out at the physiological pH 7.4. However, pH in some extracellular compartments, for example, renal tubular fluid in parts of the tubule, and extracellular fluid at inflammation loci, is sufficiently acidic to activate complement. The exact molecular mechanism of this activation is still unclear, but possible cross-talk between the contact system (intrinsic pathway) and complement may exist at low pH with subsequent complement activation. The current article reviews the published data on the effect of pH on the contact system and complement activity, the nature of the pH sensor molecules, and the clinical implications of these effects. Of particular interest is chronic kidney disease (CKD) accompanied by metabolic acidosis, in which therapeutic alkalinization of urine has been shown significantly to reduce tubular complement activation products, an effect, which may have important implications for slowing progression of CKD.

Background and objective: Establishing the amount of inpatient physical activity (PA) undertaken by individuals hospitalized for chronic respiratory disease is needed to inform interventions. This observational study investigated whether PA changes when a person is an inpatient, how long is required to obtain representative PA measures and whether PA varies within a day and between patients of differing lengths of stay. Methods: A total of 389 participants were recruited as early as possible into their hospitalization. Patients wore a PA monitor from recruitment until discharge.Step count was extracted for a range of wear time criteria. Single-day intraclass correlation coefficients (ICC) were calculated, with an ICC ≥ 0.80 deemed acceptable. Results: PA data were available for 259 participants. No changes in daily step count were observed during the inpatient stay (586 (95% CI: 427-744) vs 652 (95% CI: 493-812) steps/day for day 2 and 7, respectively). ICC across all wear time criteria were > 0.80. The most stringent wear time criterion, retaining 80% of the sample, was ≥11 h on ≥1 day. More steps were taken during the morning and afternoon than overnight and evening. After controlling for the Medical Research Council (MRC) grade or oxygen use, there was no difference in step count between patients admitted for 2-3 days (short stay) and those admitted for 7-14 days (long stay). Conclusion: Patients move little during their hospitalization, and inpatient PA did not increase during their stay. A wear time criterion of 11 waking hours on any single day was representative of the entire admission whilst retaining an acceptable proportion of the initial sample size. Patients may need encouragement to move more during their hospital stay.Objectively measured inpatient physical activity (PA) was examined for 259 individuals hospitalized due to an acute exacerbation of chronic respiratory disease. PA did not recover as an inpatient, with patients averaging 616 AE 649 steps/day. A single day of PA monitoring provided data representative of the entire inpatient stay.

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Introduction and ObjectivesHospitalisation for an exacerbation of chronic respiratory disease has a major impact on physical activity (PA). However, criteria to derive reliable inpatient PA data do not exist and current recommendations are unlikely to account for variations in length of hospital stay (LOHS) and the hospital environment. The aims were to identify the minimum wear time and number of days required to obtain reliable inpatient PA data; to use these criteria to determine how PA changes during recovery as an inpatient; and to compare PA across patients stratified by LOHS.Methods259 individuals hospitalised with an exacerbation of chronic respiratory disease were recruited as part of an early rehabilitation trial previously reported (Greening et al, BMJ 2014). Participants (mean (SD) age 70.0±9.7 years, 58.3% female) wore a physical activity monitor (SenseWear) during their stay. Daily step count and walking time during waking hours was analysed. Inpatient PA was assessed across a range of minimum wear time criteria (≥1–12 hours). Repeated measures analysis of covariance was used to compare between days and between times of day. Single-day intraclass correlation coefficients (ICCs) were calculated across the range of wear time criteria. The minimum number of days required to obtain an ICC ≥0.80 was estimated using the Spearman-Brown prophecy formula.Abstract S82 Figure 1Step count per hour as a proportion of total daily step count across an average 24 hour period. Data are reported as mean (95% CI).ResultsA minimum wear time of 11 hours (≥1 valid day) allowed 80% of the sample to be retained. All minimum wear time thresholds produced an ICC ≥0.80, resulting in 1 day of wear required to produce representative inpatient PA. Mornings and afternoons were more active than evenings and overnight (32.1% and 32.0% vs. 25.2% and 10.7% of steps/day, respectively, p<0.001) (figure 1). No changes in PA were observed during the hospital stay; ranging 585–707 steps/day and 72–83 min/day of walking. After controlling for wear time, patients admitted for 2–3 days took more steps on average than patients staying 7–14 days (997±125 vs. 597±91, p=0.036).ConclusionsOne full day (24 hours) of monitoring is required at the individual-level to obtain representative inpatient PA. A minimum wear time criteria of ≥11 waking hours is recommended for sample-level data. Wear time and LOHS should be accounted for in analyses.