| Abbreviations | Meaning |
 | HLL | Hypoplastic Left Lung |
 | HLM | Heart-lung Machine |
 | HLR | Heart-lung Resuscitation; Heart-to-lung Ratio; High-level Resistance |
 | HLT | Heart-lung Transplantation; High-L-leucine Transport; Human Lipotropin; Human Lymphocyte Transformation |
 | HLTX | Heart-lung Transplant |
 | HPA | Hypertrophic Pulmonary Arthropathy |
 | HPO | High-pressure Oxygen; Hydroperoxide; Hydrophilic Ointment; Hypertrophic Pulmonary Osteoarthropathy |
 | HPOA | Hypertrophic Pulmonary Osteoarthropathy |
 | HPS | Hantavirus Pulmonary Syndrome |
 | HPV | Hemophilus Pertussis Vaccine; Hepatic Portal Vein; Human Papillomavirus; Human Parvovirus; Hypoxic Pulmonary Vasoconstriction |
 | HPVD | Hypertensive Pulmonary Vascular Disease |
 | IAC CPR | Interposed Abdominal Compression Cardiopulmonary Resuscitation |
 | IASLC | International Association For The Study Of Lung Cancer |
 | IB | Infectious Bronchitis |
 | IBAT | Intravascular Bronchoalveolar Tumor |
 | IBV | Infectious Bronchitis Vaccine; Infectious Bronchitis Virus; Ivorian Bacilliform Virus |
 | ICOPER | International Cooperative Pulmonary Embolism Registry |
 | IDPH | Idiopathic Pulmonary Hemosiderosis |
 | IL | Immature Lung |
 | ILB | Infant, Low Birth [weight]; Initial Lung Burden |
 | ILD | Interstitial Lung Disease |
 | ILV | Independent Lung Ventilation; Instantaneous Lung Volume [recording] |
 | IPA | IInvasive Pulmonary Aspergillosis |
 | IPA | Intralobar Pulmonary Arteries |
 | IPA | Intrapulmonary Arteries |
 | IPA | Idiopathic Pulmonary Arteriosclerosis |
 | IPE | Infectious Porcine Encephalomyelitis; Interstitial Pulmonary Emphysema |
 | IPF | Idiopathic Pulmonary Fibrosis; Infection-potentiating Factor; Insulin Promoter Factor; Interstitial Pulmonary Fibrosis |
 | IPH | Idiopathic Pulmonary Hemosiderosis |
 | IPH | Idiopathic Pulmonary Hypertension |
 | IPPHS | International Primary Pulmonary Hypertension Study |
 | IPRL | Isolated Perfused Rat Liver Or Lung |
 | IPS | Infundibular Pulmonary Stenosis |
 | IPV | Intrapulmonary Vein |
 | ISHLT | The International Society For Heart And Lung Transplantation |
 | ITE | Intrapulmonary Interstitial Emphysema |
 | ITPV | Intratracheal Pulmonary Ventilation; Itaporanga Virus |
 | IVBAT | Intravascular Bronchioalveolar Tumor |
 | J | Juxtapulmonary-capillary Receptor |
 | L&H | Lungs And Heart |
 | L/H | Lung-to-heart [ratio] |
 | LAC | Lung Adenocarcinoma Cells |
 | LB | Left Bronchus |
 | LB | Lung Biopsy |
 | LBM | Last Bowel Movement; Lean Body Mass; Loose Bowel Movement; Lung Basement Membrane |
 | LBV | Lagos Bat Virus; Left Brachial Vein; Lung Blood Volume |
 | LBWR | Lung-body Weight Ratio |
 | LC | Lung Cancer |
 | LC | Lung Cell |
 | LCEA | Lung Carcinoma Expressed Antigens |