Aspiration Pneumonia: The patient's recent aspiration event and complaint of a "cold chest" are highly suggestive of aspiration pneumonia, which is a common complication of aspiration in elderly patients. The normal vitals do not rule out this diagnosis, as aspiration pneumonia can present with minimal symptoms initially.

Chemical Pneumonitis: Aspiration of gastric contents can cause a chemical pneumonitis, which may present with similar symptoms to pneumonia. The fact that the patient is 36 hours post-aspiration makes this a plausible diagnosis.
Atelectasis: Aspiration can lead to obstruction of small airways, resulting in atelectasis, which may cause symptoms similar to those described by the patient.
Pulmonary Embolism: While less directly related to the aspiration event, pulmonary embolism is a consideration in any elderly patient with new respiratory symptoms, given the increased risk of venous thromboembolism in this population.

Acute Respiratory Distress Syndrome (ARDS): Although less common, ARDS can be a complication of severe aspiration and has a high mortality rate if not recognized and managed promptly.
Empyema or Abscess: These are potential complications of aspiration pneumonia that require early diagnosis and treatment to prevent severe outcomes.

Lipoid Pneumonia: If the aspirated material contained lipids (e.g., from mineral oil or other hydrocarbons), lipoid pneumonia could be a consideration, although this is less common.
Foreign Body Aspiration: If the patient aspirated a solid object, this could lead to obstructive symptoms or pneumonia, depending on the location and nature of the foreign body.