# COLD-DOSE Protocol · Human cold-air dose-response study > Randomised controlled crossover protocol to map temperature, humidity, ventilation and duration to airway physiology, epithelial stress and recovery before product-specific AIRCHILL human exposure. - Canonical: https://www.medicalcooling.com/protocol-cold-dose-airway/ - Markdown: https://www.medicalcooling.com/protocol-cold-dose-airway/index.md - Language: en-US - Last modified: 2026-09-03T19:50:09+00:00 # COLD-DOSE ## Controlled human respiratory thermal-dose study Protocol status: planning synopsis · version 0.1 · 24 August 2026 Evidence status: proposed mechanistic study. Exposure levels, cohort size and escalation criteria are ASSUMPTIONS requiring ethics, clinical, statistical and independent safety review. ## Objective Build a quantitative human dose-response model linking inspired temperature × absolute humidity × ventilation × duration to acute airway physiology, epithelial stress and recovery. The purpose is not to discover the coldest air a person can tolerate. The purpose is to identify the respiratory exposure that maximises useful heat transfer while minimising airway stress and to establish measurable warning signals for later AIRCHILL studies. ## Design Randomised, controlled, within-participant crossover study with staged escalation and washout. Initial work should use healthy adults; an asthma/EIB susceptibility cohort can be added only after the healthy-participant safety envelope is characterised. ### Planning sample Initial healthy cohort: approximately 24–36 evaluable participants (ASSUMPTION). A smaller sentinel phase precedes full crossover exposure. Final N will be based on within-subject variability of the selected primary biomarker/physiology endpoint. ## Exposure ladder Candidate temperature levels: - thermoneutral/room-temperature control - 0 °C - −10 °C - −15 °C - −20 °C only after independent review of preceding levels Temperature is never interpreted alone. Each exposure records absolute humidity, flow, minute ventilation, peak inspiratory flow and duration. A factorial or response-surface design should vary humidity and ventilation sufficiently to distinguish cooling from airway water loss. ## Primary objective and endpoint Primary objective: estimate the exposure-response curve for airway stress. The final single primary endpoint should be selected after pilot reproducibility work. Candidate measures include change in FEV1/airway resistance or change in CC16 as a prespecified epithelial-stress biomarker. A composite should not be introduced merely to make the study positive. ## Secondary endpoints - serial FEV1, FVC and airway resistance - small-airway function - symptoms and bronchospasm - SpO2 and, where justified, gas-exchange measures - CC16 and prespecified epithelial/inflammatory biomarkers - FeNO - induced sputum in a mechanistic subset - secretion/mucus characteristics where measurable - nasal or other validated surrogate ciliary/mucociliary assessment - heart rate, blood pressure and ECG surveillance appropriate to exposure intensity - delivered gas temperature and absolute humidity at the participant interface - calculated cumulative respiratory thermal/water-loss dose ## Recovery is a formal endpoint Measurements should not stop when cold exposure stops. Repeat airway physiology and selected biomarkers at prespecified recovery intervals, for example immediate, ~30–60 min, several hours and next-day where biologically appropriate. A central development objective is to show and quantify reversibility: whether any small acute physiological or epithelial response returns toward baseline after rewarming/exposure cessation. ## Randomisation and washout Exposure order should be randomised within safety constraints. Extreme levels are gated rather than freely randomised before lower-dose review. Washout must be long enough for the selected physiological and biomarker endpoints to return to baseline. Baseline criteria should be prespecified before each subsequent exposure. ## Safety escalation An independent Safety Review Committee reviews sentinel data before opening −15 °C and again before −20 °C. Prespecified hold rules should include clinically important bronchospasm/FEV1 deterioration, oxygenation or ventilation abnormality, sustained cardiovascular signal, unexpectedly large epithelial biomarker response, serious symptoms or a pattern of delayed/non-reversible changes. The exact numerical stopping thresholds must be finalised by investigators, ethics and the medical monitor; they are deliberately not invented from unrelated sports studies. ## Statistical model Use mixed-effects modelling with participant as a repeated/random effect and temperature, absolute humidity, ventilation and duration as exposure variables. Include interactions where biologically justified. The key output is a response surface with uncertainty intervals rather than a binary safe/unsafe temperature. A candidate development metric is: Thermal utility index = measured heat-removal/cooling performance ÷ prespecified airway-stress response. This index is exploratory until validated and must not hide clinically important individual safety events. ## Visit structure Screening: health history, asthma/EIB history, baseline spirometry, contraindications. Baseline session: repeatability and thermoneutral exposure. Exposure sessions: randomised/gated temperature-humidity-ventilation conditions with continuous monitoring. Recovery: serial physiology/biomarkers. Final follow-up: confirm return to baseline and capture delayed events. ## CRF minimum dataset Participant ID; randomisation sequence; exposure temperature; interface temperature; absolute humidity; flow; minute ventilation; peak inspiratory flow; duration; cumulative dose; FEV1/FVC; airway resistance; small-airway metrics; FeNO; CC16; inflammatory markers; ciliary/mucociliary metric; symptoms; SpO2; ECG/vitals; recovery values; adverse events; stopping criteria; deviations. ## Evidence boundary Existing controlled cold-air studies demonstrate that humans have undergone short cold-air challenges into approximately the −20 °C range and, in small historical physiology experiments, colder brief exposures. They also show that high ventilation and dry air can provoke bronchoconstriction or epithelial/inflammatory responses. These studies justify a staged mechanistic programme; they do not establish −20 °C or any other value as a universal human safety threshold. Relevant anchors include the 2026 systematic review of cold-air challenge, Eklund et al. (PMID 36053365), Kennedy et al. (PMID 29178677), Frisch et al. (PMID 35391634), Clary-Meinesz et al. (PMID 1305479), and the completed CLARINET registry NCT07220928. ## Translation to AIRCHILL COLD-DOSE identifies sensitive endpoints and dose relationships. It does not replace the AIRCHILL prolonged endotracheal animal programme or the subsequent product-specific intubated human study because route, duration, conditioning and clinical population differ. ## Registration-ready outcomes and time points Proposed primary outcome (ASSUMPTION): within-participant change in the selected airway-stress measure across the prespecified respiratory thermal-dose conditions. The pilot must freeze either a physiological endpoint (for example maximum post-exposure FEV1 change / airway resistance) or an epithelial endpoint (for example CC16 change) before the confirmatory crossover portion; both must not be retrospectively promoted to co-primary outcomes. Key secondary outcomes: serial FEV1/FVC and airway resistance; small-airway function; symptoms/bronchospasm; SpO2; FeNO; CC16 and prespecified epithelial/inflammatory markers; mucociliary/ciliary surrogate; cardiovascular measures; and recovery to the participant's baseline. Exposure variables are patient-interface temperature, absolute humidity, minute ventilation, peak inspiratory flow and duration. Time points: pre-exposure baseline; continuous monitoring during exposure; immediate post exposure; approximately 30–60 min; later same-day sampling where biomarker kinetics justify it; and next-day/final follow-up for recovery and delayed events. Exact specimen times will be locked after biomarker-method review. ## Schedule of assessments AssessmentScreeningPre-doseExposure0–60 min recoveryLater / next day Eligibility / pulmonary history✓confirm Spirometry / airway physiology✓✓as feasibleserialrecovery Temperature / humidity / flow / ventilationbaselinecontinuous SpO2 / ECG / vitals✓✓continuous✓if indicated CC16 / biomarker panel✓✓kinetic sample FeNO / mucociliary metric✓✓recovery Symptoms / adverse events✓✓continuous✓✓ ## Sample-size plan The current 24–36 evaluable participants is an ASSUMPTION appropriate for protocol development, not a final powered claim. A sentinel/pilot subset will estimate within-person standard deviation, carry-over and biomarker reproducibility. The confirmatory crossover N will then be calculated from the minimum clinically/biologically relevant within-participant change in the frozen primary endpoint, its observed within-person variance, the final number of conditions, multiplicity strategy and anticipated dropout/non-evaluable sessions. The calculation and simulation code should be archived before registration of the confirmatory portion. ## Safety Review Committee charter · minimum content - independent chair plus pulmonary/critical-care expertise and statistical support; - review after sentinel thermoneutral/0/−10 °C exposure and before opening −15 °C; - second formal review before −20 °C; - review all SAEs, exposure-related AEs, individual pulmonary trajectories, oxygenation, cardiovascular signals, CC16/epithelial responses, delayed recovery and protocol/device deficiencies; - authority to continue, modify, pause, de-escalate or terminate an exposure level; - written decision and rationale retained in the trial master file. Hold criteria categories: clinically meaningful bronchospasm or lung-function deterioration, oxygenation/ventilation abnormality, sustained cardiovascular abnormality, severe symptoms, unexpected biomarker pattern, delayed/non-reversible change, or any SAE plausibly related to exposure. Numerical thresholds remain DATA GAP until the final population, equipment and medical-monitor plan are fixed. ## Decision gate A candidate AIRCHILL clinical exposure is selected only when the response surface, recovery data, preclinical endotracheal evidence and engineering performance jointly support it. The current −10 → −15 → −20 °C AIRCHILL escalation remains a provisional development assumption, not an output predetermined by this study.