Normal breathing is consisted of inhalation (sucking the air into the lungs) followed by exhalation (blowing the air out of the lungs). Every exhalation is followed by an automatic pause of about 2 second, before the next inhalation. Normal respiratory rate in a healthy adult is 12-20 per minutes. There are some conditions that may cause variation in rate and depth of respiration. Tachypnea is defined as increase in rate and decrease in depth of breathing. Bradypnea is a decrease in number of breath to less than 8-10 per minute in adults and 16 per minute in infants. Apnea is the respiratory arrest for couple of seconds. Cheyne-Stokes respiration is recurrent central apneustic episodes during sleep. Biot’s respiration is a kind of slow respiration pattern with periodic increasing 10-20 respiration per minute, without crescendo–decrescendo pattern. Apneustic respiration is prolonged inspiration arrest followed by inadequate expiration. Agonal breathing is slow, very shallow irregular respirations. Kussmaul’s respiration is a deep, sighing respiration with normal or slow rate. Sighing respiration is a normal physiologic reaction of human body to fatigue and emotional changes.

• Normal breathing is consisted of inhalation (sucking the air into the lungs) followed by exhalation (blowing the air out of the lungs).
• Every exhalation is followed by an automatic pause of about 2 second, before the next inhalation.
• Inhalation is an active process using diaphragm muscles, despite exhalation which is a passive process.
• Eupnea is the normal pattern of breathing with a rate of 10-12 per minute, each cycle is composed of:^[1]
  • Inhalation for 1.5-2 seconds
  • Exhalation for 1.5-2 seconds
  • Spontaneous stop of 2 seconds
• The main characteristics of eupnea are as following:^[2]
  • Slow
  • Regular
  • Nasal inhalation, oral exhalation
  • Diaphragmatic
  • Effortless
  • Clear auscultation:
    • No panting
    • No wheezing
    • No sighing
    • No deep breathing

• Tachypnea is increased rate and decrease depth of breathing.

• Bradypnea is defined as decrease in respiratory rate to less than 8-10 per minute in adults and 16 per minute in infants.
• Mostly in bradypnea the exhalation phase is increased.
• The depth of breathes and tidal volume may be increased during bradypnea episodes.
• The main pathophysiology of bradypnea includes:^[5]
  • Desensitization of the medullary responses to PCO₂
  • Reduction in respiratory neuronal activity
  • Inhibition of neural transmission within the respiratory center
  • Neuronal damage to the brain stem
• The main causes of bradypnea are as following:^[6]

• Apnea is the respiratory arrest for couple of seconds.
• The most common form of apnea in generally healthy people is obstructive sleep apnea.
• The pathophysiology of sleep apnea are as following:^[7]

To read more about sleep apnea, click here.

• The main causes of apnea include:^[8]
  • Obstructive sleep apnea
  • Opioid toxicity
  • Seizure
  • Asthma
  • Neurologic causes
    • Stroke
    • Myotonic dystrophy
    • Neuromuscular respiratory failure
    • Spinal cord injury
    • Bacterial meningitis
  • Pulmonary causes
    • Chronic obstructive pulmonary disease (COPD)
    • Influenza
    • Pulmonary emboli
    • Aspiration pneumonia
    • Atelectasis
    • Chronic bronchitis
    • Foreign body aspiration
    • Pulmonary edema
    • Viral pneumonia
  • Down syndrome
  • Metabolic acidosis
  • Cannabis use

• Cheyne-Stokes respiration is recurrent central apneustic episodes during sleep.
• Tidal volume has crescendo-decrescendo pattern during Cheyne-Stokes respiration.
• Cheyne-Stokes respiration is almost always due to congestive heart failure, contributed with:^[9]
  • Orthopnea
  • Paroxysmal nocturnal dyspnea
  • Excessive daytime sleepiness
  • Witnessed apneas
• Patients with congestive heart failure who have already Cheyne-Stokes respiration pattern, would have more mortality rate.^[10]

• Cheyne-Stokes respiration is mostly secondary to heart failure, but can be associated with following conditions:^[12]

• • Altitude sickness
  • Brain injury
  • Brain tumors
  • Carbon monoxide poisoning
  • Pulmonary edema
  • Hyponatremia
  • High intracranial pressure
  • Renal failure
  • Toxic encephalopathy

• Camille Biot, in 1878 distinguished Biot’s respiration from Cheyne-Stokes, named it “rhythme meningitique”.
• Biot’s respiration is a kind of slow respiration pattern with periodic increasing 10-20 respiration per minute, without crescendo–decrescendo pattern.
• Accelerations are different in a patient with Biot’s respiration:^[14]
  • Short and incomplete
  • Long and deep
  • Often interrupted by gasps
• The periods are different in length, ended to a sigh just before the pause.

• The main causes of Biot’s respiration include:^[15]
  • Pontine lesions
  • Damage to the medulla oblongata
    • Stroke
    • Trauma
    • Pressure on the medulla (uncal or tentorial herniation)
  • Prolonged opioid abuse

• Apneustic respiration is first described in 1888 by Marckwald as prolonged inspiration arrest followed by inadequate expiration.
• The rate of apneustic breathing is about 1.5 breath per minute.
• The main causes of apneustic respiration include:^[16]
  • Congenital brain-stem abnormalities
  • Upper pons damage secondary to:^[17]
    • Stroke
    • Trauma
    • Hypoxia
  • Severe brain injury
  • Ketamine (temporary)
  • Phenobarbital 
• Apneustic respiration almost always carries a poor prognosis

• Agonal breathing is slow, very shallow irregular respirations.
• Agonal breathing is resulted from anoxic brain injury.
• The main causes of agonal breathing include:^[18]
  • Cardiac arrest
  • Stroke
    • Cerebral ischemia
    • Hemorrhagic stroke
    • Cerebral hypoxia
• The pathophysiology of agonal respiration in decreased blood flow to the brain, which causes gasps.

• The most important type of disturbed respiratory pattern; Kussmaul’s respiration was first described by Adolf Kussmaul in 1874, as “air hunger“.^[19]
• Kussmaul’s respiration is a deep, sighing respiration with normal or slow rate.
• The main pathophysiology of Kussmaul’s respiration is increased tidal volume without increasing respiratory rate.
  1. Compensating metabolic acidosis
  2. Stimulation of the respiratory center which is located in the brain stem by low serum pH
  3. Lowering of the partial pressure of CO2 in the alveoli
  4. Hyperventilation
• In primary stages of acidosis, breathes are rapid and shallow, while they become deeper and slower in the later stages, which are called Kussmaul’s respirations.^[20]
• Main causes of Kussmaul’s respiration include:^[19]
  • Diabetic ketoacidosis
  • Renal failure
  • Metabolic (lactic) acidosis

• • • Heart failure
    • Liver failure
    • Chronic alcohol overuse
    • Cancers
    • Seizures
    • Intense overuse of muscles (overexertion)
    • Prolonged low blood sugar levels
    • Prolonged elevated blood sugar levels
  • Toxic ingestions
    • Alcohols
    • Salicylate toxicity
    • Uremia
    • Acetazolamide 
    • Ethylene glycol

• Sighing respiration is a normal physiologic reaction of human body to fatigue and emotional changes.
• Sigh is the elongated, often noisy expiration after inspiration of considerable amounts of air.
• Dyspnea and shortness of breath are commonly contributed to sighing respiration.
• Lack of efficient inspiration and expiration for several seconds is the main basic for sighing respiration.
• The most common causes of sighing respiration are anxiety and depression syndromes.^[21]